The old Byron mounting scheme (at least for the purr power muffler) had two U shaped bulkheads that allowed you to clamp the muffler/engine assembly to. I think the reduction drive is a little different and reduction drive/engine assembly is mounted to the bulkhead (the one just in front of the wing) and a sub bulkhead up front.

What you need to do is add a completely new firewall (1/2" thick aircraft ply) and glass it into the fiberglass fuselage. It will be quite bit further up front than the existing bulkhead (the one just in front of the wing). A buddy of mine, Fred Menna a.k.a. check6 has done a few of these in the past. With a new firewall you can then use a cup mount (Bennett or similar) to mount the G62.