[RichardJ]

>>and the HEI would therefore see a reduction in voltage.<<

Only if the battery and charging system can't keep up and supply the needed current. The voltage regulator will regulate the 13-14 volts, as long as the total current demand does not exceed the total current available.
There's nothing wrong with using a relay. It's just overkill with a basic HEI that draws less than 2 Amps at idle. If you had a big MSD box and running your 292 at 6000 a relay would probably be a very good idea.


>>You've convinced me to ditch the relay set-up and simplify the 12V feed to the HEI<<
If you are using a basic Bosch type relay, powering it with the ballast resister wire is no problem. The relay coil draws about 150 milliamps. adding 1.8 Ohms to a relay coil with a DC resistance of 75 Ohms does nothing. Relay coil pull-in voltage is 6-8volts, so if that is all the battery you have, the starter won't crank the engine anyway.


>>for something a little unusual such as a Packard terminal<<

Actually, the terminal is not unusual, but inconsistency in the terminology is. NAPA calls them a GM 56 Series. Amazon sometimes list them simply as 56 Series Terminals. Some FLAPS sell Dorman Conduct-Tite Terminals , but most seem to be assortments with junk you don't want.

>>the power from the bulkhead goes through the ignition switch, as do other power demands such as heater fan and lights. When these are active, the demand is enough that it pulls down the power available to everything running through the ignition switch<<

Your guy is correct. The current in the 12 Gauge (12R) at the bulkhead connector splits and feeds the Ign SW, the horn relay, the light SW and part of the fuse box. The Ign SW splits what current is left from the 12R and sends it in the 12P wire to the bulkhead connector ballast resistor and also splits to the other part of the fuse box that is HOT with KEY-ON.
Using a new 12 gauge wire from the KEY-ON part of the fuse box is way overkill. The stock HEI only draws about 2 Amps and besides what is left after divvying up with everything else in the cab/truck, doesn't leave enough current to warrant another 12 gauge line.

GM never used a relay for the HEI and the original wire on the HEI vehicles connecting the bulkhead to the HEI Dist Bat terminal was 14 gauge.