I have a good used set of Briggs Vanguard 18/20hp Propane Heads with the rare factory shaft mount aluminum rockers. Propane heads are identical to gas engine heads, they just have a better exhaust valve. The heads are stock and in good condition with low hours. The rockers work well using dual springs and will handle over 8,000 rpm if valve train is setup correctly. $75 shipped obo.
I also have a nice spare set of the aluminum shaft rockers. $45 shipped obo
I have another nice used OEM Briggs Denso high torque starter for sale. This was removed from a commercial Vanguard grass cutter engine. Never been on a racing motor and in excellent workong conditon. Will fit the Briggs vanguard and intek v-twins, as well as the singles. Pics available. $125 shipped
I would just use the head you have. Clean up the ports and do a really good valve job. And yes the #30 carb is the one to use. They can be hard to find but i was able to get a few new ones. A Tillotson HR would be best but not sure if your rules allow that or what class you are building it for.
The cv460 and the cv490-493 have different strokes, and mwsc makes rods for both of the cranks. Get the long rod/piston combo that matches your engines crank. You will want a cv490-493 block and crank to get the maximum CI. The cv460 blocks have a shorter jug length so you can't just put in the longer stroke crank.