Ayuh,.... A couple issues I see with the motor mounts, the 1st set were made to too big a metal,....
Donno if yer 'puter program takes into effect the .063" ribs they mount on,.....
I built motor mounts in my Islander for the 4.3l outa .090 aluminum sheet, pop-riveted to the tops of several ribs,....
The 1/4" attached to the .063" is a hard spot, 'n will tear up the lighter metal,.....
Thinner metal is Very strong, when bent into usable shapes,... structure is strength,...
Possibly won't need any wood,...
I think I'd bend up some aluminum channels, a few inches wide, 'n tall, than as Long as possible to pick up as many ribs as possible,...
Riveted to the ribs will work,....
Rivetin' to the hull will dirty the water leadin' into the pumps,....
The angles of the motor's part of the motor mount, is gonna complicate alignin' the motors, no matter how ya get there,....