You would have gotten better performance out of your HEI if you had run it on full 12 volts rather than the lower voltage from the Pink/black wire.

The yellow wire is to get 12 volts to the coil when starting, even with a mini starter one wants 12 volts to the coil when starting, then lower voltage when running, in a points type system. A lot of cars had a ballast resistor in the coil wire circuit, GM eliminated the ballast resistor and used the resistance wire in it's place.
There is a theory that the mini starters will not draw as much as a standard starter and thus not cause a voltage drop in the ignition circuit on start up, they do-it does.