I don't like the idea, if you're simply going for a rechamber and add in the conversion block in the action. The M1 was designed as a long-action autoloader. You start putting a short action cartridge through it, and you give it some free running space for the bolt to accelerate the cartridge that it was never designed for. My main concern is slamfires...some people say that M1 Garands converted to 7.62X51 are the most slamfire-prone rifles ever. If you don't think the M1 Garand's bolt has much potential for acceleration when it is not facing the resistance of a round being chambered from the en bloc clip, just hold the bolt back, stick your thumb in from the chamber, release the bolt, and try to get your thumb out of the way in time... No, don't try that, but it's likely you've already done it and know what I'm talking about...a guy only needs do this one time and only one time in their life to never forget the experience such that you won't ever do it again, and if you get to keep your thumb after having it happen, count yourself lucky ;D
I've never had one of these conversions (I don't like the idea, otherwise I might), so I don't know for sure, though. If it were me I'd go for a M1A or FAL, first, though. For the cost of a decent M1 plus the rebarrel and rechamber, you should be able to get a FAL for the same price, I'd think, if not a good used M1A. The M1 might run you $600, then the barrel a couple hundred, then the install a hundred or so, then the conversion block a little, etc... Before you know it, you could've gotten a pretty decent FAL, which actually was adapted well to the .308 (it was not originally designed for the .308, either, but it was redesigned around that round in the end...the M1 itself was not originally designed with the .30-06 in mind, either, but it was in its final form tweaked and tailored and perfected by John Garand himself for it).
Long story short if John C. Garand had any say in the matter, and had been designing the M1 around the (at the time not yet developed) .308, he would have designed the action to be shorter, to match the cartridge.
You know me, though. I'm a little obsessive when it comes to certain things with firearms and safety. I'll admit the idea at least on the surface has some merit. I've been told by some folks that I'm a little whacky for this opinion on .308 M1 Garands, before, that they used to be common for competition, etc. In the end we all have to decide what kind of rifle action and ammo combo we're individually comfortable putting our pretty faces next to and trusting not to blow up when we fire it.