O.K. So far I'm thinking a heavy pallet-like sub-structure with interchangeable steel frames for different motor mount configurations. A fixed "dash" panel with gauges and controls (ignition switch, choke, throttle); plastic (marine?) fuel tank; radiator w/ fan & overflow tank.
A separate towable subframe could be in the future...good idea.
It would be nice to be able to load an engine somehow: a clutch & driveshaft to a big pump...or a generator! Hmmm. I have an old Chevy bellhousing with mounts on the sides. I remember at school the wind tunnel fan was powered by a very hopped-up 327.
Thanks for the input, guys. I'll start measuring & drawings.

cm

If you can't fix it with a hammer and screwdriver, you need a bigger hammer.
1965 Chevy C10