Dual fans What size alternator?

I recently built a 383 for my Duster, i installed an aluminum radiator with dual fans. When the fans turn on it charges about 3/4 of the way up on the factory gauge.
It's a 60amp alternator on it now, will a 75amp be big enough or do i need to go bigger like a 90 or 100amp?
Not sure exactly what amps the fans are drawing, it has a 30amp circuit breaker if that helps any.