Which heads to run on 340

there seems to be a lot of confusion about heads here . these are casting number for 340 / 360 heads That are the same heads. " J " as far as I know are the same as "x"
just different casting numbers.
68 to 71 340 - casting # 2531894
1970 340 6 Bbl. T/A casting #3418915
1971 360 casting # 3418915
1972 340/360 casting # 3418915
1973/4 340/360 casting # 3671587
1973 360 w/air pump casting # 3671587

Cheers.