Some Lehighs and Bucks County LRs have 2 rivets through the sides of the "V" or roughly "V" shaped and slightly curved Mcaps. Most PA LRs have 1 rivet through the bottom of the inlet.
At times I have used color matching epoxy w/ cast Mcaps, but the inside surface of the Mcap is waxed and doesn't stick, but the fit is perfect. The Mcap is then riveted. When using cast Mcaps w/ thick walls, the wood is very thin and needs reinforcement.
The epoxy is not used to "fill in" a gap where the Mcap meets the wood at the rear of the Mcap.....this "fit" is nearly always perfect and easy to achieve.
I don't use many cast Mcaps, preferring to make mine from .03-.04 thick annealed sheet brass....but occasionally when building from a "kit" like Chambers, the components as supplied are used and the cast caps are epoxied on as described above.
I don't use epoxy w/ an entry pipe...finding it unnecessary to do so.