Of the three Ubertis you've had/have, what type safties did they have?
My Stoeger Flat Top and my Cattleman (Iver Johnson) have the hammer block safety. My Uberti Stallion and Model P (Cimarron) have the "Swiss Safe" safety, utilizing the base pin as a hammer block.
Incidentally, here is the original retaining screw on my Flat Top:
Looked awful, to me, so replaced it with a slotted head screw.