Petty Racing was notoruous for burying their race cars when they were done with them to prevent the competition from finding them. They even paved over the burial grounds or built buildings on top of them. They did pull richard's wreck 64 cuda drag car out of the ground a few years back from behind their shop.
As for the engines being saveable and useable, highly unlikely. but ive seen some really bad engines come back to life. It'd take sleeving, new internals(obviously) probable new heads and that's if the blocks themselves aren't pitted. Now, if they were buried in the desert, then the chances of success greatly increase