Grey Beard, the only thing unique about the mount on this plane is that I first set it up for Mag 52. I found I needed around 7 oz up front to balance, so seeing that the Mag 70 is just about 7 oz heaver than the 52, and I had one, I decided to use it. I didn't want to put a second set of holes in the firewall and the differece in widtth wasn't that great, so I milled out a set of the mounts to keep the 52's firewall pattern but accept the 70 without distortion.

It's kind of like the mount has some overly soft rubber gormlets. The first thing I thought of was, was that the firewall screws were not tight. This turned out not to be the problem. I've got a couple more of these mounts that are still mounted on firewalls without fuselages. I'm going to pull down one and swap the rubber and see if it makes a difference.