The Euro version of the frame/chassis doesn't have any of the extensions rearward from the differential, much like the GT-6.
I did some searching and found several pictures of a 1980 1500 for sale in the U.K. Fortunately they provided some detailed pictures of the area of the muffler mount. Without the frame member the muffler would fit up close to the body and is offset to the right side of the car. I can see how the muffler I have from Rimmers would fit this way.
I got an email from Carl at Rimmer Brothers confirming my suspicion that the extra frame extensions used in the later Federal (US) versions of the Spitfire will prevent mounting the muffler without modifications. He confirmed that all Mk 3, 4 and 1500s were sourced (except the Federal versions--like mine) without any frame extensions aft of the differential. This was true also of Federal cars prior to '74. Crud!
I should have saved the muffler I tore off the car, I had it out back for years and finally in a fit of 'clean up this mess', it went to the curb and the local scrap guy took it within 24 hours . It would have made a good template for my modification work. I will have to use some plastic hose and tape to figure out a solution.
More work I had not planned to do .
On a brighter note, my Dynamat package showed up yesterday so I can start lining the car interior with it.
This is a picture of a '80 1500 for sale in the U.K. Muffler fits to the right and tight to the body.
The pipe align almost straight back
A little more detail of the lack of frame extensions
For those who do let know what the frame extensions look like, a photo of mine from several years ago, just after I seperated the body from the frame.