As far as I recall I think the only Sig .45's are the 220's, 245's and the Mauser M2's. Excluding their line if 1911 style pistols of course.
I have been know to be wrong though :D
I'm curious to know what model you have, if you remember please post up the model #. :)
I think you are right, it is a 220. See my post above. It is an older model that has the european magazine drop. As far as that goes, I'm not sure it is stainless. I have a half dozen 45's and haven't played with them in awhile.
If I could figure out how to post a picture, I'd show you the gun. It is a little ugly, I broke the grip playing on a police officer course and could only find American style grips which require some crude adjustments.