Re: rope & wire halyards vs all rope halyards
I replaced the sheaves (and just about everything else) on my 30 yr old spar. to make the change from wire/rope to spectra. The sheaves needed to be a larger diameter but I got away with the same width.
At the bottom end we took out the old exit sheave boxes, welded aluminium flare tapers plates over the old sheave box holes so the halyards could then go straight to turning blocks at the foot of the mast.
I'll post before and after pics once I work out how to do it.