The Arasaka action is a strong action and you can make it into a 260 Rem or a 6.5X55 if you want and get more out of the rifle with those 160 grain bullets. If you go 260 you will have to open the bolt face to .473 from the .471 rim it has now and .480 if you want 6.5X55 Sede. The 6.5X55 swede has more case capacity and will give you better ballistics with the heavier bullets. If you looking for smaller 120 grain Nosler Partition or the Barns X bullets either would work for you. The 6.5 Jap is 2.98 over all loaded ctg and the Swede that is the longest is only 3.15 loaded. With either you will need the follower out of a 7.7X58 Arasaka rifle that is based on a rimless round like the 260 or the 6.5 Swede.
Then again if your going to re tube it you can go with anything based on 308 or the 7X57 (.22-250, 243, 250-3000, 257 Roberts,260 Rem, 6.6X55, 7-08, 7X57, 308, 7.7X58 Jap, 8X57, 338 Federal, 358 Win. And if your willing to really open up the bolt face as well as have a mag follower made the Winchester Short mags are open as well. 270WSM-325WSM