Okay, some fast figures with the Summit Racing compression ratio calculator and volumetric measurements plugged in where applicable, and compression heights listed.
If you have the Speed-Pro L-2355 40 (C.H. 2.061) with 7cc's of valve relief at .021 below stock deck your compression would be "around" 9.84:1
This is your best case scenario.
If you have Speed Pro L-2266F 40 (C.H. 1.991) without reliefs it would be .091 below deck at TDC. That yields a compression ratio of 9.05:1.
The next on the list is nearly identical but a Sealed Power 350 NP 40 (C.H. 1.990) at .092 below deck for a negligible change of 9.03:1
Then, if you want to see how bad it can be, there's Sealed Power 424 NP. (C.H. 1.912) It was probably a replacement for the 1966 440 with the 516 heads and steel shim head gaskets or the smogger truck engines of the late seventies. It could be used in a stock 400 to give .023 below deck. But it's .170 (!) below deck in a stock 440. Or 7.88:1. I hope To God you do not have this piston...
Of course, these are all subjective because block casting deck heights are oftentimes off to the high side on most Mopar blocks I've seen. So these compression ratios are almost always .1-.2 lower or more than best case figures.
If you happen to know the piston numbers, it would get us closer, but the compression test is needed regardless.
