Just to give more of an understanding on my suggestion above..
a 502 big block can fit..
http://speednik.com/files/2013/01/BM...7f-640x426.jpg
OR..a flat 6 corvair engined model
Buy This Corvair-Powered Isetta and Face Down Ten Kinds of Death
This is the engine bay factory..lots more room than expected..
http://cdn.barnfinds.com/wp-content/...600-Engine.jpg
Very simple chassis structure if looking to graft an entire subframe style conversion in..
https://s-media-cache-ak0.pinimg.com...8ea5969cb7.jpg
and..the pickup body style..which you could modify a factory stock body and end up with something much more aero and fresh looking i am sure..
https://360carmuseum.com/data/museum...44/image/2.jpg