High voltage

You're right.
Four 1034 lamps have nominal draw of 2.36 amps.
Four 158 instrument panel lights have a nominal draw of 0.96 amps
So total for headlight and tail lights will be closer to 3.38 amps. That includes the front markers and the instrument panel, but not sidemarkers of a '68 or '70 up Abody.
Likewise, a pair of 1034 brake lamps have a nominal draw of 3.6 amps.
I really didn't think it was neccessary or useful to get into this level of detail for example scenarios. In fact I prefered nice round numbers so folks could easily follow along.

There was no consideration here for any alterations to the basic load required to run an engine. The difference in electric power demand of a v-8 vs slant six ignition isnt enough to even bring up for what we're talking about.