When you are done a 40 Ford on an updated original frame will be worth more, much more than one riding on a later chassis.

I have a friend who owns two 40s, a coupe and sedan. Both run Chevy motors, Mustang II front ends, and Chassis Engineering rear springs with a Ford 8" rear axle. A very proven setup. He drives them everywhere. And that includes long cross country trips at freeway speeds.