Any benifits of 351 heads?

Stock late model 351W iron heads??? No, no real benefit. The only real difference between them are the diameter of the head bolts (1/2" vs. 7/16")....in which case you'll either have to redrill the block, or sleve the heads for them.

early pre-71 castings got slightly larger valves (1.84/1.54 vs. 1.78/1.46), but again nothing really to write home about. If you're going to change they heads, save your money and put a set of one of the more popular aluminum castings on your engine that'll really make a difference. No sense going through all that trouble for negligable horsepower gains.