It sounds as though the earlier receivers might or might not give you a problem with newer barrels. And that if there is a problem, the fix is to get the upgrade done by T/C.
Is that it, sorta?
Yep, sorta! Might or might not! If one has a very early frame, it is best to try the bbl before buying, or make sure that parts can be found to install on the bbl to make it work on the old frame!
Some have claimed that all barrels will fit all frames. If that were true, then TC would not offer to up-grade the frame to fit all barrels. If it were a fault of the frame would they then charge for the up-grade?
Truth is, for me, the earlier triggers are much nicer than the new triggers. I don't need the "easy open" conversion because the old ones are not hard for me to open with the early bbls........and I do have slight arthritis in both hands. The rimfire/center fire selector on top of the hammer 'bothers' me, but I could get used to it. Not familiar enough with it to know if there has been a problem, ie, breakage.
Now, perhaps a better late than never introduction.
Old Model Single Action Rugers have been my firearm of choice for a long, long time tho I have and use others.
I am active on rugerforum.com and it was there that Graybeard and others gave me lots of good and sometimes not so good information. Graybeard was always 'right on'!
I'll be checking in here from time to time.