No, that would not be the factory MC. Factory disc MC had one rounded end, one square end, unequal-sized reservoirs and a wire bale closure. The OEM A-body ones were somewhat smaller than on the B-bodies, but that part number was superseded, and all the rebuilds running around now are the slightly larger ones. To clarify, I mean larger as in external dimensions — I am not talking about the bore size. That varied by application, as discussed previously.
We have the equal sized bowls on our MC in our 67 cuda with factory disc. The MC may have been swapped out, but we haven't had any issues with brakes. But I've never had to lock it up either.