Thinking about getting a magwell for my fullsize 75, does anyone make one that works with the standard base pad on the Mec Gar mags, or do they all require some sort of extended base pad?

This! OP, I think Gregcotellc sells just the base pads. In fact, I know he does... so you will be able to convert your existing base plates to avoid the "horseshoe bruise" on your hand from slamming mags home on a mag well installed pistol, hahahaah! Are you installing the magwell for IDAP or some other competition or is this your CCW rig? Just curious...

This! OP, I think Gregcotellc sells just the base pads. In fact, I know he does... so you will be able to convert your existing base plates to avoid the "horseshoe bruise" on your hand from slamming mags home on a magwell installed pistol, hahahaah! Are you installing the magwell for IDPA or some other competition or is this your CCW rig? Just curious... I've never had to install one on my P-01, SP-01, or 97B because they are easy enough for a fast mag change. Adding a magwell will certainly speed it up even more though so I get why you are doing so!