Another 340 J & O head thread (what do i have?)

'72s had IIRC 8.8:1 with 915 Js. '73s had about the same compression with 587s. '73-up 360s and 340s had 587s and prior had 915s. Both '72 and '73 should be cast crank external balance with 1.88 intakes.

If you're worried about having 10:1- make sure you don't put something smaller than the stock 340 cam in it.