Rdbates,
Can't answer your question about the frame conversion, but you should be able to convert the 4.3 V6 pretty easily. That set-up is used in marine applications very frequently.
My 87 SeaRay has a 4.3 V6 that's carb and if I remember correctly, HEI distributor. It's rated "stock" at 190 H.P. set up in that manner. I believe the FI version of the same engine was rated at either 205 or 215 H.P. can't remember for sure which.
Either way, I would think you'd be able to accomplish your drive train solution fairly easily.
