Since you already have the action then its a good investment to build on , their are a good bit of aftermarket parts out their for the M-70 and the action desgine is very solid , actualy being stiffer than the
R-700. Once its blueprinted their is no reason that it shoulden't be any less accurate than a R-700 that was trued back.
Alot of guys don't like working on them becasue they take a little more work than the R-700 to setup buttheirs realy not that big of a deal , you may have to pay a we bit more for the barrel fitting due to the extractor cut having to be machined.
The best thing to do is talk to a few smiths and find one that willing to do the work , if you get sombody that sounds like they realy arn't to excited about it don't persue it any further. I have reciently gotten a barreld action back from Nathen Dagley (308 nate) and I can't say enough about the great job he did and the constsant corrispondance he kept with the build letting me know what was happening and the process of the build. Alot of guys here have had work done by Shawn Carlock and Kirby Allen and I have yet to hear any bad things about their work.
Heres a link to Nate's site