Our '84 (#3518) has the original factory topping-lift fixed at the masthead clevis pin and then is cleated mid-boom after moving through a block at endboom. And Joe's right, the existing mid-boom cleat is a PIA. Even with easing the mainsheet and vang, it's a real effort to lift the boom and adjust it. It's a feature of the two-line reefing (original system) strategy that I really don't like.
Our second "rear-facing" masthead sheave goes unused. The first sheave, of course is for the main halyard, but had I been thinking correctly with the mast down, I would have re-rigged our boom topping lift by attaching it at the endboom -first, then up to the second sheave, then down the mast and out through one of the the deck organizers. You'd have a cabintop winch for muscle on the lift as you stand on the deck, holding up the boom (and having easy access to the mainsheet, etc.). Going this route would have also enabled using it as a back-up main halyard. Keep it, Morty, it's a good thing.
Rob