Re: recommendations for halyard attachment??
Generally, I think that if the new all rope halyard will actually fit over the sheave cleanly then there's no real need to worry about it, as long the the sheave is healthy and not binding.
Rope halyards tend to be very 'oversized' for the load, simply to make it easier to hold and handle them. Small wire-only sheaves usually won't accommodate the extra diameter. This occurs mostly on smaller boats that had wire/rope halyards connected by shackle and eye spice, where the rope section was never intended to go over the sheave.
If you currently have rope/wire spliced halyards, going to all rope should be no issue...
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)