Later 348 engine
I recall the "656" casting to be a later (1964-5) truck 348 block, with plenty of meat to take an overbore and refit with larger pistons. These were cast in the waning years of the legendary "W" and are a good place to start for a new rebuild. You can do wonders with those heads and that block using newer metallurgies (valves, pistons, etc.).
Good luck!
TomK