Sounds like the rods aren't all the same length, which is common with resizing done by a novice or factory production type machinist. Performance shops , some, will find the shortest rod and match the rest...or better yet, get a longer rod...also can sometimes get away with removing more from the cap side ...say surface the cap .005 and the rod .002....but anyways..lol
Along with rod length varying ...the block is probably sloped front to back.
Don't worry about that too much at this point unless your quench is set to where only a couple pistons actually provide a usable quench distance...that would explain the detonation. Check quench distance! Jmo