Triumph Repair: Rear Body Mount spacers, crossmembers, rear frame

Question
My 73 TR6 doors have a larer gap at the top than the bottom. I have read that adding some spacers under the rear body mounts will help to close the gap. How can I locate the rear mounts to loosen them to jack the body and insert the spacers?

Answer
Best source on paper is the Bentley official repair manual.

It would be difficult to locate all of the attachment points on a car when the carpet and underfelt is still installed; the body mounts all run along the frame rails or crossmembers, and some, like the seat belt attachments, serve double duty.    The primary ones you would be interested in run directly along the two rear frame rails.

Hope that helps.