They are just a little less compression or dished like tango said.
Of course less compression means less HP.
You could get some pop up pistons and pump up your HP.
I had one of those 307 in a 69 GMC handy Van the engine sat inbetween the front seats.
I had N50's on the rear end and it would pull wheelies.
I loved that thing, it would wind up fast. Kurt