Go to Alex Hamilton gunshop site Tenring Precision. He was a large dealer for USFA and he has a couple of paragraphs about which serial numbers indicate Uberti parts built guns versus US made parts. If yo go to Lee Martins Singleaction website the is a large thread about USFA guns and one of the contributors is a large number collector and he has some information as well.
The link provided above is going to be the most complete and the most up to date info on USFA's and discerning the Uberti parts guns from the later domestic guns. You might want to also check the USFA forum on CAS City.