Short answer is I think nothing but a rebarrel and chamber job should be required. I think case heads are close enough it should work with no bolt modification. But it would be better to go to the .358 Win with precisely the same bolt face and all other dimensions but bore diameter. Then load it to .35 Rem. levels if you wish or to full .358 Win. performance or anywhere in between. Whelen is long action and not possible on this rifle.