You don't need a big alternator to run EFI but you do need a good alternator. EFI is susceptible to electrical noise so the alternator needs to be a late model design, preferably an OEM alternator. I use factory Denso alternators on my EFI cars. I use the 60 amp Denso unit on both of my cars.

You need an alternator with a fast curve in it. Alternators that we’re designed for modern cars have greater output at lower rpm than old designs. Get a denso that fits a modern era car/ truck. I also recommend using a voltage regulator instead of one wire setups.

Just how big an alternator do you need to run an aftermarket EFI? 90 amps seems serious overkill.

Running a Sniper myself with a good 'ol Toyota Denso 60A alternator as well, zero problems, charges at 13.9V per the handheld and separate can bus gauge. The Holley ignition stuff and Sniper ECU do not draw much current, basically you need 12V from a switched source to turn them on. The ignition box trigger wire is tiny so it wouldn't be able to carry much anyway.

I have the whole deal - in-tank pump, Hyperspark distributor, Hyperspark ignition box, "Sniper" TFI type coil and even the Holley gauges. I did re-wire the entire car though and it has a modern blade type fuse box. The fuel pump and headlights are on relays. Parts store mini starter, new ignition switch. I doubt the Sniper stuff would work too well with 52 year old factory original wiring.

I will say that there is not much else in my car that requires a lot of current - no electric fan, no A/C, no stereo or what have you but either way, it starts first try every time and has not had any observable electrical issues thus far.

He brings up a good point. The ONLY stuff on my car that uses factory wiring is the lights and wipers, everything else is fresh wiring.