Dear Caroline;
I think their right.
For the HEI to make the (higher) HV it would need a larger/heaver primary winding for the coil. I believe this uses a #10 wire to do this.
Besides; Why heat the choke up (waisting power) if you don't have to??
I wasn't aware of the 3 wire oil switch but it makes cents. The more the alternator works the more gas used.
Good luck.