Todd,
What tool do you use to depress the spring?  I used a small flat bladed screw driver, but am thinking it may still be too thick to allow the front foot on the base of the sight to slip under the pin. I ended up having to punch out the roll pin, seat the sight and then tap the pin back in while pushing the sight back against the spring..  I shoot a classifier with it in two weeks and since it's sighted in I'm going to leave it alone until then.  After that I'm sure that just a little work with an emery board will have it fitting like it should.

Scott