I have posted on the Gunsmithing Forum the following - how hard/difficult is it to convert a pre-64 Model 70 in .30-06 to a .458 Lott assuming the action is unaltered? What problems to expect? Who would you have do this?
Thanks

Well for starters open up the bolt face to magnum size, replace the extractor claw or mill it, open up the feed rails, replace the follower and possibly follower spring, re-barrel it to .458 Lott, bed the action and add some cross bolts to keep the stock from parting ways. Not bad but some others here with more experience than I can tell you more of the details but this should give you a list to start with.

I have a prewar M70 30-06 that was made into a 416 remington. The boltface was opened up and the action top was milled out to recieve the longer cases. Mine feeds and ejects fine but you will have to tweek or change the spring and follower. No crossbolts on mine just a brown precision stock all bedded in. My gun turned out very light so I needed a brake to make it shootable. Not sure if I like the noise and muzzleblast.