How many amp Alt needed with Jeep fan mod?

[Arl37]

69 C10 with 350 crate HEI auto trans and no AC. Installed Jeep Fan mod and now when ever fan kicks on the needle on voltage gauge pops over to max as long as fan is running. Gauge is original. 195 thermostat and 195 temp sensor for gauge. Fan runs pretty much all the time once it kicks on. Fan supposedly draws 30 amp. Have 78 amp alternator from 93 Silverado. ( Got that alt off forum as recommendation). Before fan mod, gauge was in middle of gauge pretty much all the time. Afraid my alt is not keeping up with draw and battery not fully charging.
What size amp do I need with jeep fan?