Fastening trysail track to mast

[atmarineservices]

In finishing the refit of our Flicka 20, we are adding a trysail and seperate track to the mast. I have some questions as to the fastening of it. Rivits, or drill and tap. If the drill and tap, is fine thread preferred due to the higher thread count per inch, and drilling through such thin materiel? I saw in a recent post that Brian Duff specced NO RIVETS for a mast splice. Any more inout would be greatly cherrished. Thanks!!