1972 20' c.c. rebuild

[Rbphipper]

Ready for new transom. Can't afford Coosa cause of shipping to N.J. is crazy. Planning on using 2 - 3/4" marine fir from Lowes, but worried its too heavy with these newer motor weights. Should I be concerned? Any recommendations? Also planning to raise transom to 27" and decking 2 1/2" based on my readings on this site. I've attached pictures of where I'm at. Should I remove old 1/8" inside transom glass and just go new layup, or is the old glass ok to bond too? It doesn't seem brittle. Also, why are the hollow stringers open to the transom material? Seems they should be glassed closed. I appreciate anyone's knowledge on this project. Thanks