My Catalina is a 1988 and the sheaves on the masthead were cracked. Halyards were line not cable. I replaced with ball bearing for main and plain bearing for the spinnaker, topping lift and jib. Jib is on furler.
Wire to rope halyard sheaves often have a smaller groove, to fit the wire, within the larger groove, which is sized for the rope. Did some research and learned that the edges of the small groove are bad for rope. They abrade the covers and cause premature failure.
When I went to all-rope I took my aluminum sheaves to a machine shop and had them turned for all-rope. Came out nicely. Lost maybe 3/16" diameter at most--not a critical amount, and preferable to buying new aluminum sheaves. Although acetal sheaves aren't that expensive.