I have the same situation you do. ''82 Dehler DB1 3/4 ton IOR boat, very tapered fractional bendy mast, and a bank of 3 sheaves for the center jib and 2 wing wire halyards. All the jib halyards were fraying badly and needed replacing.
I checked the sheaves and they are not the U-channel groove style suitable for only wire, nor are they abraded badly... and my 8mm (5/16") Validator II replacement line appears to fit nearly perfectly in them... which means it is probably larger than optimal size for that sheave diameter. The old wire halyards were 3/16".
Still, I am going to run it for this summer season and see how things go. I tied on my shackles w/ buntline hitches, the line strength is rated at over twice what the old (and fraying) wire was, so I anticipate no problems with that. I am not stripping the cover, mainly for longevity but also for added protection since i''m not absolutely certain there will be no chafe issues.