The reason for this modification is that I do not like any of Contax_G to Sony_E or μ4/3 adapters. So I planned to make my personal
G-Planar 45mm with its own helicoid for ease of focusing and E-mount without an another adapter. I happened to have an M42->μ4/3
adapter with helicoid, which extends from 12mm to 18mm. There is not much space left between the lens block and the M-mount base,
which should be less than about 12mm between in order to focus to infinity. It looked doable to me, then I started my own conversion.