915s or 596s

It's my understanding that they are basically the same heads. Maybe some minor differences but that's it. I have a set of X heads (894's) a set of 915's and just sold a set of 587's. The 587's did have slightly smaller exhaust ports but other than that they all looked very similiar except the X heads had 2.02 int. valves. That being the case I'd say do whatever needs the least work cause in the end they will be the same or real close.