I have a Siamese Arisaka and tried making up ammo for it using 7.62x54R brass: same base diameter for all practical purposes as the 8x56R.
No dice.
Expansion at the base was plain scary, even with very mild loads.
A lot of these rifles, and especially thew Siamese Mausers made for the same cartridge, were converted to handle the .45-70. The .45-70 is .505" at the base, .608" at the Rim. MUCH easier to convert to 8mm Siamese.
As mentioned, there is absolutely ZERO parts interchangeability between the Siamese and the Japanese Arisakas. It is the same DESIGN , but DIMENSIONS were changed everywhere in order to make the Siamese rifle completely a different critter. This did two things: (1) it prevented Japanese rifles from being a source of spares for the Siamese rifles, and (2) it gave the Japanese a captive market for spares for this UNIQUE rifle.