joe's correct, especially if you use an open spacer as opposed to a 4-hole. You can indeed make your own, using a gasket as a template. Make it from a nice piece of 1"thick wood. Use a holesaw to cut the 4 holes. Make sure the wood is flat and parallel when you're finished making it. Many times, the air/fuel mixture will make the turn from the carb throttle bores into the manifold runners easier with a spacer without crashing into the bottom of the manifold and creating turbulence.

The wood will insulate the fuel in the bowl from manifold heat.