May or may not help.
Ambi Safety removal - 1911Forum
sig sauer 1911 ambi safety
I've never owned a Sig 1911.
My Kimber was tough to get off.
The right side is held in by a pin that slides into a groove of the right side.
Single side hammer pin
Ambi hammer pin
You had to remove the left side to get the right side off.
Check out those links and see if it helps.
If not, check out 1911forum.com and see if you can find more info on it.
Found this too..
Thread: Removing thumb safety on SIG Sauer 1911
Started 1 year, 8 months ago by peter_nield
Hi, I thought I would try to disassemble my new 1911 Target this evening but didn't get very far. I couldn't remove the thumb safety despite considerable wiggling, pushing the plunger back well out of the way and even tapping on the pin from the right side of the pistol with a brass mallet. The safety just wouldn't budge although it would quite happy engage and disengage. I had the slide removed ...
Reply 1: Removing thumb safety on SIG Sauer 1911
bdavis replied 1 year, 8 months ago
The safety should not be all of the way up. There is a notch about halfway between down and up where the thumb safety can be removed. Don't worry about the plunger all the plunger does is keep the safety down or up. Pull out on the safety as you move it from down to up and it should come out. Good luck
Reply 2: Removing thumb safety on SIG Sauer 1911
peter_nield replied 1 year, 8 months ago
Thank you sir, worked a treat.