Thanks for this, Jonathan. I've really struggled to get the mainsail all the way up, and have taken to loosening the outhaul, tightening it when the sail is up. This sounds like a very good solution.
It was actually quite a problem in my first season with the new boat. I'm almost always single handed and am used to motoring clear of moored boats and drifting while I get the sails up quickly. Last year I kept having to tie up to mooring buoys because it took so long, with resulting crises when the tidal current kept pointing me in the wrong direction.
Matt had also suggested silicone spray to lubricate the track, which I'm about to try. Another contributing factor, which I failed to notice until the end of the season, is that the slots on the BRe spray hood are misaligned, so the halyard rubs quite badly. But I think your cleats are differently positioned from mine so it might not be the case on your boat.
Can I ask why the Cunningham, or downhaul as I have always called it, needs to go through the boom, necessitating v accurate drilling, rather than around it... I say this without checking my boom, of course.
Thanks again for sharing this idea.