Run the carb backwards; it won't mind at all. When you do that, everything falls into place except the choke (which is backwards). I simply run the automatic choke. Both Chevrolets and Mercury's had automatic chokes. The only thing you have to watch for is they both offered a choice of divorced (actuating element on the manifold) and regular (actuating element on the carburetor) automatic chokes. I have done it both ways and they both worked well, and the parts needed only minor modifications. A slight bend of the actuating rod on the divorced style and a shortening of the heat tube on the regular version. If you're lucky enough to have the carburetor choke type match the type on the manifold. it's super easy. I have a number of small base 2G's around, so I have always been able to match them up. I have never tried to mix 'n match them.
Chevrolet 2G's are nice, since the fuel inlet is on the side matching the stock fuel line. Other makes (B-O-P) have front fuel outlets.
One last thing : the base of the Chevrolet carb has cast-in heat passages that can cause vacuum leaks. I have had a batch special aluminum plates made up to eliminate this problem. PM me and I'll send you one for postage (about $2).
And "40Cpe" is correct; the carburetor will not run well with the stock Load-a-Matic distributor. You can either run a converted SBC distributor or (my choice) an old Mallory dual point (they have "the look").