Can rivnuts fix my mast?

Incredibly fiddly, as predicted, and a little compromised.

In the end I  used the spreader hole to get inside with a lead mouse, stood the mast up and rattled like hell, exiting via the spinnaker uphaul sheave hole; then pulled in reverse so that I was able to pull the bolt out the hole and into place. Sounds easy but it took forever because I started with the wrong method -- trying to drop the bolt directly from the jib sheave above because I hadn't though it through properly and just went for the biggest entry point. Head-wrecker.

In the end, no ladders or platforms needed. But next time will definitely heed advice to use stronger fishing line, and also more highly coloured. Dull brown, lightweight line was the biggest cause of distress, with one bolt lost -- temporarily -- up the mast due to a break. (I am now doubly fluent in swearing and general crankiness.)

Bolts (6m) are a bit undersized for the hole due to the limit on the lug, and I could get only one nut on each bolt because of the shape of the lug and the need to leave room for space for the securing pin for the bottle adjuster, which still needed a bit of gentle hammer-persuasion to fit home.

Couldn't find nylon washers, but I did use Duralac and it got everywhere. Also used threadlock on the threads to help the nuts, now dead tight, stay in place. I'll need to monitor them carefully... here's hoping!

I hope this account helps anyone considering a similar operation. Thanks again to all for the very sensible advice.

PS: I was thinking when preparing at one point to fail with the bolt method (desperation being the mother of invention)... Would it make sense to pull a washer against the inside of the enlarged hole, then superglue it in place to give a new, smaller hole to fit the usual-size rivet? Also fiddly, but I think it could work generally where rivets are preferred but the hole has become too big.