I think 80+ Amps, but you need it to putout a large percentage of the rated current at low RPM.
This can be done by changing the crank/alternator pulley ratio. When choosing the pulley ratios you want to make sure ther alternator is not over reved at peak engine RPM. This is one reason I like the newer Denso alternators usen on most of the new Mopars. The Denso alternators are rated to 14,000 RPM, so even with a 2:1 pulley ratio you should be good unless the engine normally revs way over 7,000+ RPM.
You will also have to upgrade the wiring. As a minimum run a 10-AWG (or larger)wire from the alternator output to the battery (should go through a fuseable link too)while also connecting the stock alternator output wires. The new wire will create a parallel circuit to the battery, but will have lower resistance so it will carry more of the current than the stock wiring. The only problem is the stock alternator gauge will not move as much so you should add a voltage gauge to monitor the charging system.
The stock electronic '71 and up voltage regulator should work fine to control the alternator, but you will need the plug-in connector for the alternator.