There are a number of ways to check this, so am showing a in general way with simple measuring tools.
First I set a rule on a protractor and secure at 31.5 degrees, the rule can't go very deep into the mag well. By setting at the desired angle I can see if it is 31.5 deg, more or less, or correct.
Then by placing two parallels on the deck you can balance the bottom of the protractor so it is parallel to it, and align the rule in the center of the ramp.
Then you can get a good look at the rule and how it lines up. Another thing is the depth, you can arrange the rule so it is at say .400" and see that also. I didn't in the pic. The frame ramp on my blue guns are blued as I have re-blued them along the way, and like the polished blue ramp and leave it, why not? :)
I've read that the ramp angle between the .45ACP frames is different than the angle for a frame being used for a 9mm build.
What are the difference's and what issue's might one might run into building a 9mm on a .45 ACP frame?
I'll have to look it up again, but from memory, the 9mm uses a steeper angle. IIRC, it's something like 20 degrees as opposed to the 31.5 degrees for the .45acp.
Mr. Hoag told me it's doable, but by the time you get done you might as well buy a 9mm.