There are plenty of used but in good condition pre-64 Model 70 rifles floating around, even the pre-War variety, which have better workmanship, and buying a compete rifle for the action is cheaper than buying the actions you mention. If you can't find one, let me know and I may be able to help you out.

As far as the .270 is concerned, the only problem I see is the availability of match grade hunting bullets in that caliber. If you wnat to produce really accurate results, you need to take a step down to 6.5 caliber (6.5-'06 or 6.5X65 RWS) or a step up to .280 Remington or 7X64, both of which calibers have access to a whole range of really accurate bullets.

Then, of course, you would be abandoning the Jack O'Conner connection.