There is but it takes a very brave person to do it. You can cut off the original and weld in a piece of aluminium the shape of the later crankcase bosses. I have had it done to at least two crankcases which had the original boss broken off and the later design is much stronger than the original. It is often forgotten that the engines were being developed throughout the whole production run. Although financial trouble caused troubles with some aspects of quality to-wards the end the 'D's were developed after consultation with many riders and there are several aspects of the later engine and suspension which are better than the early ones. Note that I have no axe to grind here as I have 'B', 'C' and 'D' engines. I seem to remember that his 'ighness the 'iggins gave an improved design for the pivot in MPH some time ago .