I know some have trouble fitting new exhausts but mine have been little trouble recently, and they came from Coventry Spares. I think the problems may come down to the oft repeated phrase that no two Vincents are alike and this is amplified by changes to standard compression and cylinder height and wear and distortion over the years. Probably the most helpful tip I have found is that the required flange you have to fabricate on the front pipe if the nut is supplied loose may not be exactly perpendicular to the curve of the pipe where it seats in the he head. I loose fit the pipes before making the flange with the muffler and fasteners in place and use tape or some method to approximate the angle of the flange. Then you can carefully make the flange, (not forgetting to put the nut on first). You can find home made jigs described for this process, but it can be done without them. There is enough material on new pipes to massage this fit to get it just right couple of times if the first attempt is off a bit. Don’t make the flange any bigger than necessary, get the angle right, and you will have no more problems fitting up the pipes in the future.