Thanks everyone for the responses. So according to 3 different serpent suppliers around the world (I literally emailed all the English speaking countries listed on the Serpent website as well as the China one (as that's where I live at the moment, but thinking it would be a hail Mary move) the consensus is that the car was not designed for the F104pro foams after all. ErikJan is correct in that it was designed for the wider F103 foams and equivalent. The Australian supplier initially thought there was no such thing as F104 foams and kept telling me that I needed Tamiya foam wheels and tyres, to which I kept saying I was running them. Only for them to say that it should be correct then, and for me to rebuild the rear end over and over, until they explicitly said that foam was for the F103, and rubber for the F104. I sent them the Tamiya link to the F104 pro and they suddenly realised where our wires were getting crossed.
China got back to me (in English as he studied in Sydney Uni) and said he had both the wide and normal track car on his desk in front of him and that as Dan said the rear end is the same across the SF2 range (by the way Dan the difference in width was almost 20mm with the F104 foams, and there was no way to add almost 20mm spacers to the rear axle). China's car was riding on matrix foams (no idea what they are, but they will be sending me a link this morning for me to look at). And then the Singapore said that it needs the offset of the F103 foams, but they are hard to find now.
So it seems the problem is solved. I wish Serpent had simply made a note somewhere to say that xxxx was the recommended wheels and tyres in the first place. Cause the existence of the F104pro foams threw all assumptions out.
Last edited by Mr Brooksy; 07-03-2017 at 08:02 PM.