Wonderful work, and I visit your website often. I also restore these old machines and quite a few BSA Mk 1Vs, Mark Vs, and a few Mercurys have passed through my workshop in the past. I've managed to hang on to a couple, a Mark V and one 'mystery' BSA which has no Mark stamped on it, just an X above the frame number. It must have been a military bike in bygone days as it arrived with leather weapon straps and faded green paint.