X O U or J heads on a 416?

The letter designation doesnt mean a whole lot. Its the casting number you should be looking at. The exception would be X heads since I believe they were always the same casting and used on early 340's.
I have had O and U TA heads. There were J's with 2.02 and also 1.88 intakes. Basically any 340 or 360 head would be a good start and there is not a ton of difference between them.
Personally I wouldnt bother putting stock heads on a stroker build. You would be way ahead of the game with a good set of heads, even on a stock stroke engine.