My gun is actually a type 44, a short carbine model of the type 38 6.5 round. The Arisaka military round was a semi-rimmed cartridge. There was a 5.6 X 50R round that some follks used to open up to 6.5 X 50R.

Anyhow, most important thing you've illuminted for me is that Hogdgon states that a .264 will do. Again I'm not surprised as the Arisakas had a reputation of having generous bore dimensions.

I guess my step 1 is to slug my newer Arisaka 6.5 barrel to determine it's land-groove dimensions and then go on from there.