Mast holes
To mount something on your mast, you have a number of choices. Pop rivets may be the easiest -- no need to worry about the inside of the mast and they are pretty strong. If strength isn't a really big issue (eye straps along the boom, for instance), you can use a tap to put threads into the hole that you drill. (Use coarse thread taps, not fine -- the screw will hold better in the thin aluminum walls if there's more material left behind after you've tapped the hole.) If strength IS a big issue -- mast mounted winches, for example -- you must put something on the inside to keep the bolt/screw from coming out. A fender washer, lock washer and nut will be sufficient in most cases. For high load applications like a padeye used for a vang attachment, a backing plate should be used.In all cases, you must isolate the fastener material from the mast/boom material or you will get galvanic corrosion. The aluminum will eventually get eaten away at the point where it contacts the stainless steel. Coat the contact points of the fastener (and washers) with Life Caulk or Loctite before you install them.As far as having the halyard jump out of the cam cleat, I think Bill probaby keeps the halyard around the winch and/or cleated where the winch is after he finishes fulling tensioning the halyard. Then, when it's time to drop the sail, it drops without interference from the mast cam cleat.The mast cam cleat is just a temporary way to secure the halyard. It isn't taking a huge load, so you can probably get by with simply tapping holes and using the largest diameter fastener that'll fit in the cam cleat mounting holes.By the way, you can get a tap kit from places like Home Depot -- it'll come with a tap of a particular size and thread type, a little handle and a drill bit to get the hole started. Be sure to lubricate the tap as you turn it. Any thin oil like 3-1 works fine.