If I remember right, the LT500 has a conventional shock (angled forward instead of backward like your Full-Floater), and the airbox is behind the shock, like on my 92 LT250. If so, the airboot wouldn't work for your 87 LT. Something for you to double-check if you haven't already. I put a 38mm carb on my LT, have to heat the boot in hot water to get it over the carb! Barely fits over mine, so don't think that would work for your 41.5mm.
Lookin good on the rebuild!