Some of the other mounts look like they've got possibilities, too.
RGPM-25M4 is a 2 piece mount that has 2 bolts per base - that might hold almost as well as the 1-piece. RG18D-25L and RG18D-25M are described as "Extra strength for magnum springers", and each has a receiver pin built into it.
They all look like excellent rings for the price... thanks for the link!