Check your masthead sheave. If it has a groove in the center for wire you should change it otherwise the halyard won't last as long.
If the sheaves are shaped like a U with a little groove in the bottom of the U for the wire, then its alright for all rope.
If the sheaves are shaped like a V, they should be changed as they will damage the halyard.
Some of the Catalina's that were originally rigged with rope/wire halyards were not spliced but rather the wire was nico-pressed around a thimble and the rope was either tied or eye spliced to that. Usually in those cases the sheaves were too small to accept rope at all.
If that is your situation, you will have to replace the sheaves as well as the divider between them.
I agree with SD that Sta-Set X is a good economical alternative to high-tech line. A little more complicated to splice and a little stiff but good line.