I done my 19ft transom in less than 50 hours, what took the most time was the epoxy resin "curing" which is not calculated in the rebuild time, each epoxy laminate takes 48 hours to cure for sanding
You can cut the outside transom skin 3-4 inches in around the outside than chip out all the plywood, sand the inside skin free of plywood, bevel your 3-4inch radius right around, vaccum the whole lot, wipe the whole lot down with acetone
Cut your plywood and test fit however many layers you would like to use cut various shapes for maximum strength and make sure no two cuts align between the layers of plywood thickness
Remove the plywood, fillet the radius both sides and the bottom you want enough glue to fill the voids once the plywood is pushed into place also smear glue all over your internal transom skin, now place the first layer of plywood up against the front transom skin than use clamps, screws, bolts and tightly press the front transom skin against the plywood
Next smear glue all over the back of the plywood you just installed, prepare your second layer of plywood to go in and push it in now screw or clamp this second layer of plywood to the first layer (you can use screws from the outside on this layer of plywood) let it cure, remove screws
Grab the transom skin u cut out at the beginning you'll notice the inside of the skin will have remnance of plywood sand all of this off, next smear glue all over the the second layer of plywood or the rear facing piece of transom plywood, grab your transom skin and clamp or screw it to the rear transom plywood, let it cure
Remove the clamps or screws
Bevel the radius of the transom skin 3-4 inches, wipe with acetone, clean any glue that has squeezed out you can just sand it off with a grinder, now cut your fibreglass cloth/mat in strips going from thin and progress to wider, start glassing the joint where u originally cut out the transom untill u build up enough thickness u can sand the whole transom flat and level ready for paint or flowcoat
You are done