There are basiclly 2 different cylinder heads that have been used on production "A"
engines from 1964-1990. A small port 273/318 head and a big port 340/360 head.
There have been only 3 different valve configurations for these. 273/318 with 1.78"
intake and 1.50" exhaust, one for the 1968-1971 340 heads with the 2.02" intake
and a 1.60" exhaust these size valves are also found in 360 j heads and the other
configuration is 1972-1973 340/360 heads and some 318 high proformance heads with
1.88" intakes and 1.60" exhaust. most of these can be I.D. by the casting numbers and the letter codes on the outside of the heads. If you have a stock 318 with original heads on it they will be the small port heads with the 1.78" intakes and the 1.50" exhaust valves. I hope this helps . Cheers.