My choice would have been the SOHC 6.2 V8 that is an option for some Ford trucks. Cast iron block, stock aluminum heads and a nice auto trans as part of the package. Poke & stoke it and you could have 427 cu in or more and an engine with 500 HP at 6000 RPM all day long with no reliability problems.You probably could have had b for that price if you didn't rebuild the block, but no 'wow' factor.
Just 'oh, another one of those'.
See https://en.wikipedia.org/wiki/Ford_Boss_engine for more info