[gumby79]

Roller cam, reduced friction and you dont need the additives to keep the cam alive fuel is not the only thing to consider in hypermiling.
2010 oil report

4 Barrel carb a 500cfm carb only has 125cfm per barrel summit racing used to have a 350cfm 4b Holly avaliable (was going to put it in place of the Holly 4412 /500cfm on grandmas 61GMC 1/2T 305b v6) . if you can stay out of the 4 it is smaller more tunable. In anEdelbrock all4 are the same size. I'd go with a rodchester ,supper small primary huge secondary .dirve it on the primary.
Msd 6 Digital has built-in 2stage revlimiter primary for broken driveshaft protection secondary for lowning out the vehicle
Timing retard add nock sensor or micro switch to the carb linkage + your desired toggle.. and a 20° retard in start-up mode
Rpm
the 350 I had in my79 K-20was happy @400 the alt was happy at 600 rpm https://alternatorparts.com/alternator-pulley-size.html theas guys have the overdrive pully for your alternator to allow your desired ultra low idle