if you can find a 260c alternator,they have a 75 amp externally regulated alternator that'll bolt straight onto the a series bracket & uses the same style wiring.this should handle the demand for the amp,& not be too hard an upgrade.or 1200rallycar has a conversion for a
80 amp ford falcon alternator on his web site.
both options should do the job you need.if you go for the 260c alternator,grab the regulator off a b310 sunny,they are adjustable,so you can get the right amount of charge to the battery.