You got a good deal for a good running 350 for 50.00. Id expect to pay 300.00 or more for a complete running 350, or 150.00 or more for a runable shortblock.
or 150.00 for a complete rebuildable 350, so Id say you got a good deal.
As far as the 307 goes, if its a good running engine...or even a rebuildable, 100.00 is a decent price. especially if your doing a #s matching restoration & need a correct 307.