As an owner of a Mk12 built by Monty, I would suggest against it. @WobblyPossum
They pin the gas black on the top, not the bottom. When pinning barrels on bottom, that clamps the block down against the gas port. When pinning from the top, it doesn't. The result is a naturally leaky gas block. When I sent them emails to point out the issue that my gun was under gassed and sent photos clearly displaying carbon soot that has escaped the gas block and gathered around it, they refused to acknowledge that as an issue. They did agree to ship the upper back and open up the gas port, but securing the gas block in a conventional fashion that's doesn't make it leak would be preferable.