Re: AeroCraft York 1960ish Transom, Stringers, Deck
Based on this interior pix:
It would appear that there will be minimal impact to using 3/4" deck plywood, particularly if it's available in 1 of the preferred choices. Aurauco, douglas fir or MDO ply. You will loose 1/4" of the height difference between the seat & bottom of the steering wheel. If you were able to salvage any of the interior side trim pieces, they will need to be adjusted. If you saved just the vinyl for patterns for the interior side trim, it will also need to be adjusted.
There will be additional weight & cost involved w/ using the 3/4". But sometimes that is a stock item & is cheaper per sheet then 5/8" or 1/2" because they are special order items.
If the distance between your stingers is less then 24" (appears to be for the center & outer, but approaching 24"+/- to the outside chine) you may find 5/8" is a nice alternative to either 1/2" or 3/4". Lighter weight during construction & after installation then 3/4", thicker (stiffer~more rigid) then 1/2", and in some cases the extra 1/8" won't affect interior trim height as much. Depending on how you layout the interior & use the boat, 5/8" spanning 24" w/ poly resin & CSM on the backside, & resin, CSM, 1708, CSM and tabbing on the topside, may be sufficient.
If I could get Aurauco in both, I'd choose 5/8".
I'll be damn lucky to find it or Douglas Fir in 3/4" even on special order. I think I'll be using MDO for mine in 5/8" ($45+/- per 4X8 sheet) if available as a special order when I am ready. In my tin it wouldn't be much different, but in my FireFlite, the stringers are almost 3" wide (hollow fiberglass, NO stringer wood

) and only @ 18" center to center, 15"+/- clear span. I can usually order 3/4" MDO ($55+/-) easily....