what is the better option?

i have a 1971 truck 318. it uses oil and the valves ratlle when cold. ive found a running 318 in a 79 winnebago for 300 dollars with 79000 miles on it. would it be best to just buy the 79 or replace the valve stem seals and reseal the 71 engine. is there much of a performance difference in the two? thanks