The simplest fix will be to make up a spliced lead to connect the Ign.1 and Ign. 2 terminals together at the back of the switch. Do nothing at the starter. Your switch was designed to bypass the nickel-chrome resistance wire that used to be connected to the I-1 terminal while starting, to give the coil full voltage during cranking with a straight copper wire, not a resistance wire.

I would reccomend using a #10 wire, both as a 12 volt source from the battery to the ignition switch, and as a power feed wire from the ignition switch to the HEI. That's how GM does it on all their wire harnesses for original equipment HEI cars and trucks. Use a #10 fusible link if desired to protect the ignition switch voltage supply against short circuits.
Jerry

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