Would a compound rest from and atlas 10 inch lathe fit on an atlas 6
inch lathe, mine is the old style rest and would like to update to the
newer style.

If you can get a copy of "Model Eng. Workshop", July 2003, a UK pub. Read
the article "Improving the Conquest" (a lathe). Mr. A Sinclair suggest
doing away with the compound rest all together for the sake of more
stiffness, less chatter and better cutting off. The down side is when you
want to advance the threading tool at 29 deg. However, I designed a
threading tool holder that over comes this objection.
Don Warner