Right. Let's say you find a truck 390. It has 410 pistons in it so the piston is down the hole. (Just as a 360 uses a long rod and a 390 piston, again resulting in a down the hole piston at TDC). Low compression, & lack of quench are power killers.

Having said that, these are big engines, and they do make a fair amount of low end torque. If you changed to a later type cam, "RV" type perhaps, a stock T or S manifold, a 600-650 vacuum secondary carb and some good headers, you would be running some decent power. IF you found a sound motor to start with....

BUT, the newest FE is from 1976. Many rainy seasons, and perhaps lots of wear in whatever you find.

I would always do a rebuild on such an engine, running or not. Too much work involved to end up with a smoker/leaker/dead cylinder pooch.