I have recently completed a 3.90 R200 diff swap into my 71 240z and also purchased a techno versions diff mount which I believe is very similar to the R/T mount. I also purchased the poly GM mount so I can get rid of my factory lower mount. The problem I am having is that I cannot get the bolt lined up to attatch the gm mount to the steel bracket. If I bolt the gm mount to the bracket first then I'am off at the diff bolt holes.

Has anyone with this diff mount had to modify their's to make it work? it also seems as if the poly mount needs some trimming done to it aswell.

I have read multiple times that this is a straight forward install, and I have triple checked everything and I just can't seem to find what I'm doing wrong?

Just did one of these on a friends 260. We had some of those issues you are talking about.

If you are trying to do this with the diff still in the car you are doing it the hard way.

With the diff out its a very simple job.

We had to place the GM mount in first. Then bolted one side of the mount up.

We then used another jack to push the mount into the possition on the other side.

The fit is very tight and worth the trouble.

Good luck..

John