Oh yeah. Pontiac big blocks are approximately small block Chevy sized (okay a little bigger), but make a lot better torque. I don't know if very many V8's will pull a heavy truck and manage 20 mpg, but maybe with a good enough overdrive, anything's possible.
You could even stroke the 400 with a 455 crank I think. For options on the Poncho motors, checkout Indian Adventures on the internet.
Good motors. I love my 68 Firebird's motor. Amazing torque, enough to make even a 3.08 feel good.
