Should be no problems.
Expect to pay around $300 - I did check this out a couple of months ago to have a 30-06 rebored to 35 Whelen in a Remington 7600 pump. I did contact two gentlemen (Steve Holborn - ON, and I believe Ron Smith from AB) and both could do it. The only problems is that you will have to be patient as these guys are very busy.
I don't have the information on them handy but probably could dig it up, if interested - just send me a pm.
Duke1
PS. You probably already know this but just in case, the 35 Whelen is a necked up version of the 30-06 where the 243 evolved from the 308 and so did the 358.