So Nathan, as an example, if the gage reading was 140 psi, the ratio would be:

Gets you close, but...a longer stroke, larger bore size, or longer valve open time will give you more volume of air to compress, resulting in a higher compression gauge reading, compared to an engine with the same mechanical compression ratio, but with a shorter stroke, etc.
The above method is valid for getting in the ballpark, tho...just not in the big leagues.
It is better than nothing.

I feel your pain, I was/am in the same boat. A lot of what I read and going of my dyno sheet (I finally studied it ) was that mine was close with 16 initial and 36 total @ 3k rpm. I pulled my carb off more than once to re-set it to baseline. And I put some new carb and spacer gasket on mine and cranked it down tight after it was warmed. Pretty steep learning curve if you're on your own, even more so when your sweating about your new engine. I never got to the point where I could get a decent idle under 1100 rpm though. I hope you get her dialed in right and you can run pump gas in her!