the isolation of prop loads on a crankshaft that IS
NOT DESIGNED to take prop loads.

This is the kind of problem I was fishing for in the original post --
something I hadn't heard of, but constitutes a show-stopper.

I like that two-into-one spark plug idea. If that's feasible, I'm a
LOT less attached to magnetos.

could a GM engine attached to a short manual trans 1-get a dry sump
and 2-be flipped upside down and have a stout racing trans take the
loads. i'm thinking the dry sump/upside down engine makes a more
normal looking cowling. I vaguely recall piston luftwaffe planes
having inverted Vs.

as for not getting your money's (or weights) worth of hp running a
502hp Gm engine at 1/2 redline, remind me again, how much does an
O-720 cost, weigh, and what hp does it put out?