6.5 Swede is ok.., but I would also vote for 6.5-06. Good friend recently did one of these in his Mod 70 30-06, and it is simply amazing! 6.5-284 would be another to look at. And being long action, the bullets could be loaded pretty extreme OAL. Heck, I run 260 Rem, and even it surpasses 6.5-55! But still a sound cartridge.

For any any of these, all you will need is a barrel. (Is also rec. an aftermarket, machined barrel nut & recoil lug. Just inexpensive insurance). You will also require an Action wrench, Barrel Nut wrench & at least a Go Gauge. Good luck.