What is the minimum CH in a smallblock which would keep the rings out of the pinhole???

The method Diamond uses, around 1.325" but, you can stack the rings tighter
and go with less. That's just their preference on the ring spacing.

Edit: That was using 1/16 x 1/16 x 3/16 ring pack.

My current configuration has a 1.21 with custom pistons. I'm looking at a combo which would only be a .975. Is this way too short????

I'd say YES but, almost everybody has shelf pistons for SBC @ 1.00"

.975 is way short

I have a .975 comp. ht with my 4" stroke and a 9" deck block and I won't do it again when I build my next motor.

Why ? What's the trouble ?

BTT, It looks like the answer is somewhere between .975 and 1.20. Any more inputs with experience and recommendatoons?????

Not small block but.
The last Custom Diamonds I purchased was at 1.32 which didn't need oil rail supports. The Current Wiseco's at 1.29 do need them. So somewere in between...

Cab, I didn't even think about the wrist pin size. My current combo with a 9.56 deck heigth, 3.91 stroke, 6.4 Alum rods and .927 pin provides me the 1.21 comp heigth. You're right a pin of less than .927 would provide some additional room.
I'm just looking for a safe number to plan for my next build. At this juncture it's easy to also vary the rod length. I was planning on a 6.5 rod which may not work.

I've had two different sets of dished JE's at 1.12 .One set had support rails for the oil rings & the other did not..