Please clarify whether you have a stock gm starter or an aftermarket ( hi-torque) unit and what style of ignition switch is being used. My experience tells me the original 56 ignition switches do not have a terminal that is usable to supply power to the coil when cranking.

Aftermarket hi-torque starters generally do not have the R terminal mentioned earlier in another post. They only have 2 terminals 1 12v battery connection 2 crank connection. Having a combination of original ( early) ignition switch and aftermarket starter will require a relay in the system that is operated when cranking, the wire to the starter to intial the crank also operates a relay which in turn switches battery 12v to the coil.

Terminal 86 12volts from ign switch when cranking
Terminal 85 good ground connection e.g relay mounting screw when screwed to metal surface only
Terminal 30 12 volts from a permanent battery source
Terminal 87 12 volts to HEI

In the case of a stock GM delco style starter connect the R terminal direct to the HEI. Originally this was done on points style distributors to supply a high level of volts direct to the coil positive on cranking bypassing the rest of the car and ballast resistor if used. Reading other posts I believe a relay and base will set you back a few dollars but a worthwhile investment.

Hope this helps
Andrew


1950 Chevrolet 3100 in Oz