No idea how fixed on (pics helpful) but often enough with pop rivets - easy to drill out, but to reinstal need a pop riveter (although can often get by with self tappers, but not sure if they enough for a mast
But as you imply boat a bit of a kit
, my big question would be - does the winch work? if so I would leave alone (or move to the bottom of your list)..........simply because you sound like will have plenty of other stuff that does need doing.
My top tip as you go along is to ask self "do I really
need to do this job"
and if the answer is simply "I would like to" then drop it behind the list of things that are needed
............cash and enthusiasm (aka will to live!) both have limits - spend what you have of both wisely