Sheave/rope priority

[JohnV]

Hello--
I have to replace the worn-out rope halyards in my recently-acquired Alajuela 33.
There are 3 pairs of bronze-bushed aluminum sheaves in the masthead, and they are grooved for wire/rope halyards. I'd rather use all-rope.
My choices seem to be to either replace the sheaves, or to switch to rope/wire halyards.
Acetal sheaves of the correct dimension (about 3 1/8" in the slot) on the market all seem to be too wide (I need 5/8"). New aluminum ones are out of the question due to cost.
So-
Is it ever viable to have the old aluminum slots turned down to a rope groove? Can a local machine shop do it or does it require a specialist? If so, know of any good ones?
Or is going to wire/rope, with its various potential disadvantages, going to be my most realistic option, economically?
Thanks for any ideas.
John V.