I've read that a few Arisaka sporters have been made in Finland using Arisakas obtained from the Russians at the end of WW1.

IIRC, these rifles were originally purchased by Britain, intended to be used as trainers but never having been used to any great extent {or at all} as American-made P14's arrived and served that purpose. Some P14's were of course also used as sniper rifles by the British. The Arisakas were then sold or given to Czarist Russia during 1916, some then falling into Finnish hands in 1918.

Maybe the British sporters were made with some of these UK-purchased guns?

And yes, with no recoil shouldere the 6.5 bout the extent of what you want to chamber the thing in. Heavier kickers need not apply...demonstrated when the Japanese added the recoil shoulder to the 7.7 version.