Sure happy to help Peter. I install pick-ups every week or so and have two to install tomorrow, Monday. Both Baggs Anthems into two 12 strings.
Some background and recommendations first though:
We see it frequently where a major manufacturer relied on third party proprietary electronics that may only last 5 - 10 years in an otherwise heirloom built guitar. The pick-up fails and owners are sent scrambling for replacements that will use the very same modifications to the instrument that the original manufacture did to the instrument to make it whole again. Some of these guitars have massive control panels in holes in the sides..... and at times no suitable replacement that uses the same form factors.
They are not always in luck and replacements can be anything from nonexistent to few and far between leaving no one any choice on performance, tone, etc.
With this said I would strongly recommend that no one build a guitar around a specific pick-up. You will be sorry eventually if you do.
The good news is there are lots of aftermarket pick-up choices that do not modify the instrument in an irreversible manner and create a dependency on an electronics company that may go treats up in time.
So I can tell you what we tell our clients and what they do with the information and I can also tell you what I've done for myself with my own 3 month old now Martin CEO7 that is my retirement guitar since we are a Martin certified warranty center shop I wanted a Martin for myself. When I started building I gave my three Martins away to force myself to play my own stuff thinking I would get better faster if I had to suffer....

This is my first Martin in 20 years and I love it.
All of my recommendations can be installed and removed without a trace except for the reaming of the output jack hole and the Anthem requires two holes in the saddle slot.
Recommendations:
1). For flat picking simplicity, great tone and fast, easy installation that most here could do with some advice the K&K pure mini is hard to beat. I'm home right now and have one in the box downstairs in my home lutherie shop to install in my new Martin CEO7. Yes that's right the guy who installs pick-ups for others picked the K&K for his own ax.
They are inexpensive around $110 from Amazon and delivered the next day where I live.
To my ear this pup is best for folk, bluegrass, rock and blues. It does finger style OK but I think there are better choices for the finger style player.
A huge advantage of the K&K is it's passive meaning no battery to ever worry about. Many of my clients are gigging musicians and when you need a pup you likely are a gigging musician even if it's just a jam with the ole high school garage band members who are still kicking. My gigging clients have me changing batteries all of the time because they worry about losing a battery during a gig. No worries with K&K. No battery at all.
Downside: People struggle with the placement of the transducers and working with CA blind in the box. FYI transducer placement is not critical.... provided that one is close to the intended locations of the three transducers. Dave uses a jig and vacuum to hold the transducers I do it free hand.
2) Baggs Lyric even easier to install than the K&K and no super glue required. Just be sure to hit your bridge plate with some 220 paper to smooth it out, wipe off any dust well before using the peel and self-stick for the mic. That's all there is to it.
This pup is best for a lush sounding instrument with a finger style player. I find the mic does feed back if you are not careful with amp or PA speaker placement and being a mic you will hear noise from impacts with the top, heavy picking, etc.
I have a Lyric in one of my Heshtone prototypes a L-OO that I play or played the most before I got my Martin. When I get near my Dumble clone that I play through most of the time (RedPlate that I had custom made for me by my friend Keith and I love this amp) I can get some Dumble sized feed back that is not good.
If it goes in a lousy sounding instrument true to form you will get lousy tone so best for a decent sounding instrument.
$160ish IIRC
3). My favorite for some years now is the Baggs Anthem which can do all styles of music well, has a UST (under saddle transducer) and the mic from the Lyric. Downside is installation it's nearly like installing two pick-ups so it takes a little longer. There are tricks to how to install a UST well AND the saddle must be reviewed for suitability and proper fit for a UST. The saddle must also be milled down 0.032" to keep the same action because of the thickness of the UST.
With or without the Baggs preamp that you said you want to avoid it can sound wonderful and in terms of tone it's my number one pick. They are pricey though $260 and up.
You can play any style of music with this pick-up and adjust it for some of the best performance and tone available in my experience.
4) The new Baggs HiFi is excellent but I've only installed a handful and know what I think of the great tone but I need feed back from customers before elevating this pup higher which it likely should be. I do have concerns of double sided tape for installing the various elements many gigging folks may gig outside in high RH and that does not mix with tape generally speaking....
These are medium difficulty to install and the tone is about as good as I have ever heard. Installation is reversible as it is with all of these except the Anthem requires holes in the saddle slot (2) for the UST making the Anthem not totally reversible.
Others like Fishman can be very good and the bottom line is that many of the offerings are excellent. These are simply my favorites that I have a lot of experience with.
There are less expensive pick-ups but we don't recommend preferring to stick with main stream choices. There is also a tendency for those doing the recommendations to apply our own bias in all that we do and say... to when we are asked about something.
My clients are not cheap.... an inexpensive solution is not at all high on their CTQ (critical to quality in Six Sigma speak) list. Instead they want reliable, time tested and safe to gig with inside, outside, you name it. They also don't want their prized guitar hacked up for someone's proprietary solution only to find that pick-up company perished and they now have unsupported 10 year electronics in a 100 year heirloom instrument. Not good.
Lastly there are lots of good choices including many that I did not mention. These are what I've gone with and done hundreds and hundreds of installations and never had any negative feedback (pardon the pun) from clients with these choices.
So for me K&K for flat picking, Lyric for finger style, Anthem for anything and the HiFi I have my eye on and think that tonally.... it may be the best there is I just need more experience with it AND it's over $400 clams.
Hopefully something here will be of value to you Peter.