Long time shooter.  My 16yr old son wanted to start shooting matches and he's been doing defensive pistol matches at our local range.  We're going to shoot a USPSA match next weekend and I'd like to shoot my S&W 45acp, full size 1911 and I have a Dawson Precision IPSC classic division magwell for it.  What division should I be signing up for, the guns completely stock other than the magwell which I can remove.  I'm not looking to win as much as just have fun shooting and finish as high overall as possible.  I shot my first match the other day at our local IDPA style match and took 7th out of 27 with a stock Sig X-Carry.  I was pretty happy with that, only guys who beat me were running carbines, optics, or race guns.  I'd like to try the 1911 now that I'm hooked.

Uspsa Single Stack division. I think the IPSC magwell is smaller than the ICE magwell which is legal in the division.

Appendix D5 of the rule book does not mention magwells

Only that your pistol fit in a box of these dimensions

Yes, handgun with empty magazine inserted must
fit wholly within a box with internal dimensions of 8 15/16” x 6” x 1 5/8” (tolerance +1/16”, -0”) (8.938” x 6” x 1.625”) (227.01mm x 152.40mm x 41.28mm)

https://uspsa.org/documents/rules/2019_USPSA_Competition_Rules.pdf

Don’t know if can access without membership

You'll be fine shooting single stack with that.