MOTing a car in the ages of 65/70 period normal has no restrictions, they dont get checked for CO's either, well mine never does, but i like it done to see the readings to keep an eye on settings.
Two friends of mine have mustangs one 65 with side pipes and 70 shelby with them on it and they have had no trouble's moting.
Last summer while looking for my wifes wedding ring at goodwood i bumped into Alan Mann and sir John Whitmore, i had a chat with him and Allans mechanic! while doing so i had a good look around the 65 coupe they race. It too had side pipe's like that of the set up as the eleneor ones. the box goes to the rear axle hanger then out let comes forward. but i have seen others on ebay for $70.00 per set. Also on the subject of leaf springs, the car had very nicely forged-out spring sets and remained having rear drums. now if this car can get round goodwood in 50 seconds then its pretty well to say any roadgoing mustang is well equiped with this set up!
The mechanic work shop is directly across the carpark to the Topgear location in Dunsfold. The Mechanic remembered seeing my car parked at topgear and so i said i would pop in some day to see his set up. So my advise would be to get in touch with them for info and settings because that carwas going round the track on rails.
http://www.plansmotorsport.com/contact/
