340

a 1973 340 came with 1.88 valve "J" heads, heads would work pretty good on a 318 as is.

for the 340: You should upgrade to 2.02" valve "J" heads or maybe have those heads reworked for the larger valves.

If you are doing a lot of street driving with the car, you should have hardened exhaust seats installed in them so they will live with modern lead free fuels.

Bob