You can get the info yourself, if you are motivated.
Buy one of these: SIG P320 Insert | Quality SIG Sauer-Compatible Parts | JSD
Smash it flat in a hydraulic shop press; then get out the calipers!
A lot of people like to build the things they use, be it guns, cars, houses, furniture, or planes and such. There's this satisfaction of using the things you made, that you know inside out as a result, all their little idiosyncrasies or strengths (and how far you can push them)... And as such things go, the JSD MUP isn't that easy to mess up to begin with.I see the allure to have something "off the books" but in all honesty... it looks like you will spend just as much doing it yourself as it would cost to just buy a Custom Works FCU @ $349
Add in the risk of messing up the $99 insert... and it doesn't seem like it makes a whole lotta sense to me. lol