I'm not so sure you need to replace the firewall. I think I read somewhere
that Chip Hyde uses a 1/8" firewall in his Hydeout pattern plane and that's a
heck of a lot bigger than your U-Can-Do with a lot bigger engine. You just
need to have more reinforcement and more area to glue to. From your
pictures it looks like it wasn't glued to too much of the fuselage. I've got a
SuperTigre Bluehead 60 on my Matrix 40 but I triangle braced it and put some
glass cloth in the corners behind the firewall. Also did the wing hold down plates.

tommy s