Are you sure your orientation and terms are correct? The right side is pretty straightforward on these (if it is a B44R frame), it is the left side that is a reverse-threaded monstrosity. With a very special stud and toothed keeper that complicates a simple issue.
If you don't have a parts book to look at, you could go to www.bsaunitsingles.com
and look at the spares manual
for the B44R. It should show you what you need.
As Kommando sez, different components over the years, so earlier and later pegs won't play together...