I recently replaced the two plates - Austin and valve clearance specs - on top of the 100-6 valve cover. The replacement plates and rivets came from the usual supplier.
Unless I am missing something, don't waste your money on the rivets. The rivets supplied are made for an application much thicker than the combined thickness of the valve cover and the plate. This is not the first time that I have seen this type of rivet, and usually installation goes well. In this case, I tried to install the rivets by holding a metal cupped plate on the top and a punch underneath - carefully hit with a hammer. The rivets have a small hole drilled in the bottom side, and they should spread at that point, firmly holding the plate in place. But the hole is not drilled nearly deep enough, so the rivet spreads without holding the plate tightly against the valve cover. So the plate is very loose when the rivet is spread. It also looks terrible, from underneath. One could take a very small drill bit and try to drill that hole deeper, and one could also cut off the rivet to make it shorter. But I doubt that the result would be satisfactory.
So after drilling out the supplied rivet, out came the pop rivet tool and pop rivets. That worked well. The only problem with that is that the pop rivets have holes in the top instead of the smooth, rounded look of the original rivets.
Unless I am missing something, don't waste your money on the rivets. The rivets supplied are made for an application much thicker than the combined thickness of the valve cover and the plate. This is not the first time that I have seen this type of rivet, and usually installation goes well. In this case, I tried to install the rivets by holding a metal cupped plate on the top and a punch underneath - carefully hit with a hammer. The rivets have a small hole drilled in the bottom side, and they should spread at that point, firmly holding the plate in place. But the hole is not drilled nearly deep enough, so the rivet spreads without holding the plate tightly against the valve cover. So the plate is very loose when the rivet is spread. It also looks terrible, from underneath. One could take a very small drill bit and try to drill that hole deeper, and one could also cut off the rivet to make it shorter. But I doubt that the result would be satisfactory.
So after drilling out the supplied rivet, out came the pop rivet tool and pop rivets. That worked well. The only problem with that is that the pop rivets have holes in the top instead of the smooth, rounded look of the original rivets.