I am surprised the heads do not have 3/8" threaded holes. Your next best bet would be in the intake manifold , near the stat housing. There should be a threaded port there.Ok,just about to fit a new engine.
Couple of small issues,
No provision for oil pressure sender by oil filter so fitted it at back of block by dizzy(easy fix).
No provision for water temp sender between 1&3 cylinder on heads,so where do i fit sender for accurate reading.
If i fit it on stat housing will it only read when stat is open?
Any where else on block/inlet manifold or water pump it can be fitted?
Oil pressure at top of china wall is fine. Only oil temp need come from the port above the oil filter.