EFI, electric gauges, fan etc all running on a 63 amp here - no problem at all. Gauges will only draw 1-2 amps max. EFI itself including injectors will be <5 amps, fuel pump max 10 amps, but under normal load they pull <6 amps continuous. You aren't adding much extra load with EFI in reality. Most modern cars with ABS, EFI, Stability control, Heated front and rear screens, heated seats, AC etc will have a 110amp alternator at best. Your current 100A alt will be just fine.