While the Type 38 6.5 Arisaka is among the strongest rifles ever built (mostly because of the quality of steel used in the pre-war years) it does have, like many military rifles (the SMLE for example) a generous headspace. For the handloader, this is a problem that makes for very short case life. The best solution is to start with virgin brass and neck it up with a 270 or 7mm expander ball and then size it in the 6.5 Arisaka die only enough to allow snug chambering. This will set the headspace on the shoulder instead of the rim. For subsequent reloads you should only partially resize, keeping the die from touching the shoulder.
A less ideal technique is to fire factory ammo and partially resize thereafter, but only expect about 2-3 reloads before seeing partial case head separations.
The Hornady 129 gr 6.5mm bullet was designed to duplicate the Arisaka load. With this weight bullet, start with 38 gr of IMR4350 and work up to 2300 fps.
I tend to develop loads using slow powders to gain a bit of safety cushion. I doubt one could put enough 4350 in that little case to bend anything.