I have run a setup like shown on the Speedway site, though I fabricated it myself, for 20+ years. It does work reasonably well, though I've wondered about the intake getting too hot in warm weather when pulling a hill.
There is enough gas transfer back and forth due to rhythmic pressure differential to heat the intake manifold. I have an Offenhauser two single barrel manifold. It has provision for a factory-style heater for when you're running a stock exhaust manifold. I just took a quarter inch plate and drilled a couple of holes in it for the pipe fittings. I believe I used 3/8" copper tube. Works well even in Wally Montana winters, which we have where I live. On the humid coast it suffers from carburetor icing at idle until the thermostat opens. But that was a problem when it was stock. The carb(s) has a thick heat insulator under it.
