Yes, the MG parts have been visible in the DB for a while. As for availability, I don’t think I’ve ever seen them listed as “in stock” (likely because they haven’t completed manufacture of them yet?)…

With regard to them being GP parts? Well, I’ve looked into the 750’s metal gears before, and while they are the same size, the diameter of the cross pin is different between the two, which means that the internals of the diff case must be different to accommodate each respective cross-pin assembly. I didn’t go into detail with looking at the outdrives, but those are likely different too, so probably no shared parts there either.