The pushrods on the later bikes are 10mm longer. The STM cylinders for instance come with a 10mm spacer which is dropped in to the piston before being fitted if required.
you could knock something up easy enough. The rod diameter is 8mm. Get some 8mm rod, or even a 8mm bolt and cut a 10mm length off, slip it in the piston and try that.
A tip though, cut it from ferrous so you can pull it out if needed with a magnet
