RE ; 17 inch carved tops general numbers.
The perimeter re-curve areas are about .125 to .25 in the center for X braces
and .125 on the sides , .165 on the ends and .195 in the center for parallel. This is for spruce..cedar go a bit thicker. Lutz can go a tad thinner in the recures.
The backs are usually around .125 recurves to .195 in the center.
At any rate me woulden't take much more than .125 off of either side. in the recurve area.
Me gotts no idea about plywood plates other than
Re rib widths...
anything much wider than 3.25 and the top end starts to becomes thin and weak not to mention its getting kinda big to hold.
anything less than 2 5/8 produces a weak voice instrument lacking in the depth and richness of an arch topper.
Depending on the size and position of that oval will determine if you gonna go with parallel or X's. Of course you could always use bent braces but you really gotts to know what your doing.
Even though me hears tell they are good tops, you can do what ever you want with that Acme including burning it.
thus spaketh
?admablessings