Michael,
The old alternator was a 40 amp unit,not enough for high output ignition and fans,etc. I run a ford 65 amp unit ,it is the bare minimum, I should have gone bigger to 100 amps.
Msd= 10 amps
fuel pump=6 amps
electric rad fan=18 amps
heater/defrost=15 amps
lights=10 amps
This is the minimum I use about 60 amps. i don't like to run maximum output on anything so to have some safety margin I would like at least an 80 amp unit.
Just my 2 joules worth
Perry.