Donnelly's book on cartridge conversions says to use the .270 and head swage it.
Yet, on the very next page, for the 6.5x52 Mannlicher Carcano, he says use the .220 Swift.
Given that the Italian and Japanese cartridges are VERY similar dimensionally, I don't see why you couldn't make a stab at using either .220 Swift OR even 6.5 Mannlicher cases.
The rim might be a bit small, but the Japanese rifles had quite a bit of bite so it might well work.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.