I was thinking about alternative drivetrains.  Here's a suggestion.  Since
Honda motors turn CCW (looking at the accessory end) and so do Corvairs,
why not a Honda 4-cyl. and the Corvair transaxle?  The Corvair transaxle
has withstood V-8 conversions--most of the internal parts of the '66-69
"Saginaw" transaxles used beefy off the shelf "big-Chevy" 4-speed parts.
It was available with ratios of 3:08, 3:27, 3:55, 3:89 and 4:11 and, if you
are lucky, can find or build a posi-traction differential.  They also can
be further beefed-up with 4-spider gears.  (There was a rather large
motor-home manufactured back in the late 60's early 70's called the
Ultra-Van which originally used a Corvair drivetrain, so it will hold up.)
There were kits to put Corvair drivetrains in the early air-cooled buses,
so the axle adapters are already out there.  Some of the engine mounting
parts may work as well.
The Honda motors are quiet, efficient and bullet-proof.  There must be
plenty of used motors around.  What do you think?