The front pin should enter in the lock mortise and come out on the opposite lock panel. On some rifles the exit hole is underneath the sideplate, but many rifles like this don't have side plates so it just comes out in plain view. To attach them you need to make sure your guard is inlet in the right position in the stock, clamp it, than drill (preferably with a drill press) through the stock and lug. Than you can push (or tap) the pin in and cut it to the right length and it should hold your triggerguard tight in the mortise. There were lots of rifles that pinned the rear or the triggerguard also, but also a lot that used a screw. Pick up a copy of Foxfire ( I forget what number) and you can see a good article in there documenting a young Herschel House building a plain southern mountain rifle. He builds pretty much everything except the lock and barrel and it is a very interesting look at a person who was to become one of the more known muzzleloading gunsmiths of the day.
I have seen the kit you talked about in person, I live not far from Track of the Wolf. I personally feel the 54 caliber is awfully large for a rifle like this, I like the caliber, but I don't know how well it fits this style of rifle. I would personally drop it to 45 or 50, both of which work fine on deer if the range and shot is reasonable. On the other hand it is your rifle and it would make a light weight powerful hunting gun. Plus, who's to say that an original didn't get freshed out to the larger caliber. Have fun in any event.