The exhaust crossover port is for quick warm up. The heat riser closes, then forces exhaust thru to the other side. This warms up the mixture for quick warm up. The restricter is there for two reasons that I know.
The passage way could not be cast smaller.
These engines are used thru out the world for cars, generators, marine, etc. Different applications.
In SC Kalifornia, you don't need it. Some people block them off completely and lock the heat riser open. Install the restrictors on both sides.
P.S.Remove and block off the EGR.
Source your vacuum advance from the manifold. Set to 36* total timing at 2500 RPM, and let er rip.
