On both my Sierra's the poly diff mount and rear have always been very close to each other. But now on my re-shelled car it's even worse, the arb is really tight against the diff mount. The diff mount already has the countersunk bolts fitted and even has the thin plate between diff mount and diff removed to gain some clearance, but that is not even enough.

I just don't get why these aftermarket diff mounts are not designed with a bit more clearance. I think there might be some history there, as originally the poly diff mount was first designed by Mc2Racing in the US, for the Merkur XR4ti. That car doesn't have a rear arb that runs so close to the diff mount, so no issues there. I believe the companies in the UK producing these diff mounts simply copied the design one-on-one, while they could have made an update to it to fix these clearance issues.

I am unsure what to do with it, as I don't want to run the car without rear arb or with the stock diff mount.