The oversize piston needed to be turned down. The initial problem was how to hold it. A block was prepared to pass through the gudgeon pin with a hole at the base to take a threaded rod. A location boss was then turned to fit inside the piston. The piston was then pulled hard down onto the boss using the threaded rod.

Here we see the piston mounted in the chuck of the Harrison M400 lathe. The piston ran true to within 1 thou (0.001") without any extra adjustment. A rounded end piece of tool steel at a low feed rate produced a very fine finish which did not require further finishing.  The original Leyland pistons were turned both tapered and oval. This later piston  was only tapered however the casting around the gudgeon pin bosses is heavily relieved. I assume the relief which the limits the effect of the expansion of the additional material around the gudgeon boss made the oval characteristic unnecessary.  The ring grooves were deeper on the new piston compared with the original piston. As the old (but new rings) were to be used the ring grooves were not touched.

Here we see the new piston on the left now at the +030" size with the original troublesome +030" piston. Now all we have to do is put everything back together!