valve stem height - need some help

For some reason, I was thinking the OP’s heads were the 210cc version(RPM copy).
Probably because I wouldn’t have considered the 265cc head as a viable option for his application(383 Street car).

Imo, the 265cc “victor” style head is a very poor choice for what the OP is describing as the finished product.
A part number, or a couple pics would clear up what he’s working with.

If the 265’s are what he has, I’d look into sending them back and buying some Stealth heads instead.