[Brian]

When fitting aluminum heads to one of these engines one needs to take extra care.

A bit hard to actually get what you're saying; have you fitted replacement longer studs to suit the heads? If so, some of them could be slightly cocked. They can be straightened in situ. Or, are you using the original studs, having removed the old heads, and discovered the new heads won't slip over them and down into place? Please elaborate and we can advise further. And....welcome!