Yes mate the gasket does most of the bigger 'A' series Mazda engines. Yes you're right too about the MA going to round port exhausts.
After playing around with Mazda piston engines for over 20 years now, I'd probably recommend just using the whole MA engine. There isn't a lot of gain putting the MA head on, as you increase the compression ratio and probably blow out the headgasket again! The MA stroke is different and the piston isn't flush with the top of the cylinder block, but in your VC it is. The VC engine does run a bit nicer though.
If you do go up to the MA, look for a motor out of the series two 626 rwd or later 929. the flow rates were the best out of all the engines of the time. The best way to tell if find an engine already out of the car, is to look on the front of the cylinder head, just under the distributor moulding. There should be a four digit number cast into the head - 8057 is the good number.
Another quick trap on the VC, they is usually two inlet manifold gaskets in your VRS gasket kit, pay particular attention if you replace it as the VC was the only one out of all of them that uses a balance port between the manifold tubes. When looking at the manifold, they are located between the very outer tubes(cyl 1 and 4) and go to cyl 2 and 3. One gasket lines up nicely and the standard that does NA,MA etc exposes those ports and it engine won't run and you'll pull your hair out trying to find the fault! Seen many a VC engine pulled apart again looking for something else!!
Too many Mazda's in the collection. 4 Mitsubishi's, 6 Toyota's and now 3 Datsun's as well.
Putting together a Mazda/Japanese motor museum. New bigger venue for the museum has been bought, watch this space!