I finally had enough of researching every adhesive known to man and grabbed a tube of E6000. I figured in the event of the worst case scenario (things didn't stick together) I could remove it easier than anything else. I smeared a layer of the stuff on the plastic plate of the Limbsaver and on the rubber surface of the OEM pad. Then I clamped them together and left the assembly alone for three full days at the end of which I set about shaping the Limbsaver to match the outline of the OEM pad using a bench belt sander. I didn't do a terrible job and I comfort myself knowing that there was no good way to attach the assembly to my Miles Gilbert Recoil Pad Installation Fixture.

Bottom line. The E6000 worked. The Limbsaver is very soft and pliable. Launching 12oz projectiles no longer feels like a 3" Magnum 12 gauge.

Here's a pic showing how it turned out. You can see the glue line between the plastic plate of the Limbsaver and the rubber of the OEM pad. I may get after that with some sandpaper. The fit between the two is actually very close. The glue is just what slopped over onto the exterior of the OEM pad.



Many thanks to everyone who offered their suggestions.