All 915s cast O U and J all say 360 on the head but did come factory on 70-71 340s w 2.02 valves. Not all Js are 2.02s though. All the Js ive actualy pulled off of 360s have all been 1.88s
I have witness the same thing when it comes to J heads on 360's all the ones I have ever seen have been 1.88 too. Disappointing too, you see they are J heads only to take them off and they stock size. LOL