Al,
My first wilwood was mounted as yours was, it failed. The second came with instructions to mount it on the frame. It chattered & failed.
I made my own mount for the third one. It is holding up fine. Another issue with some Wilwoods is that the piston unscrews from the rod. This was a part of my problem with the second one. I really believe the vibration from the two mountings you have tried could be the cause or a part of the cause of the failure and the chattering. It won't cost much to try a solid mont to the engine before embarking on a transmission & clutch removal.
Good luck, Paul