Dual fans What size alternator?

What have you got for wiring?

Completely factory?

MAD ammeter bypass

Aftermarket?

Start by reading this article:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

If you don't have 'a lot of other stuff' a 60A MIGHT do it, but the wiring needs to be "up to snuff."

Even Ma knew that the factory wring was marginal. If you can find the documentation (it's in some of the factory service manuals) of what is called "fleet" or "taxi" wiring, this was done with factory 65A optional alternators. It involved abandoning the original ammeter wire and running them in through the firewall in separate grommets.