Well I got an email response from Alex who stated he didn't think it would fit and that they are delivering one that will fit the XCR but did not say when or how much. I believe he meant that they are developing one.
Well with a 50:50 chance he could have said he didn't know or support why he didn't think so, I was just asking a simple question and figured I would get a more definite answer rather than leaving me still wondering.
I've got it for you. Just compared my M1a and my gen2 gas block XCR. No joy as to it working. The dovetail on the M1a measures .25" across while that of X is .43" +/-. Ergo the M1a spec stuff is way too small.