The 336(x) heads are very similar to the other early to mid 70's large chamber smoggers 441 487 920 etc.
If they have screw in rocker studs, guide plates and 2.02x 1.60 valves they could possibily be from a 1971-1972 350 Z28 LT1 motor (330hp 255hp). if they have pressed in rocker studs 1.94x 1.50 valves they are from a bread and butter base passenger car/truck motor. Get them checked for cracks before investing in them. Modest power in stock as cast form.