They are just two small little metal rods. Do I just insert the bottom cap into the mast, then drill a small hole for those two fasteners, hammer them in? Do I need to weld them on the outside? Otherwise they will just come out no?
No welding required. My oldest (and used) cap requires the pins for security. Two newer caps intended for my new mast didn't come with pins.
Drilling a new mast to match up the pins will be a challenge to match up the holes. Note to self: drill new holes, and ignore the factory holes. Use the usually-discarded mandrels from pop-rivets as your new pins: 5/16ths-inch rivet, I recall.
Perhaps the heat from strong sunlight can force the caps out using internal air pressure, IDK. (And, afterwards, pull water from the step inside the mast at night--again--IDK).
Mine was a very tight fit. I used an random orbital sander to bevel off the outer part of the cap. I then got it in with a rubber mallet. I'll keep watch on it but I may be good with that. But if I do use the pins I just drill holes and hammer them in? They don't fall all the way in or fall out? Obviously I drill the holes slightly smaller than the diameter of the pins.