I am considering putting on a new high output or (higher output) alternator on one engine. Do I need to buy a new voltage reg, that is made for the specific alt??

Your alternator is internall regulated, nothing extra required.
The wiring from the alternator to the starter is only an 8 or 10 guage (orange wire on 4 wire Mando). You may want change this to a larger size if you're getting a very large alternator.
Gary

They make neat adjustable regulators to carry the heat load of the increased amps and recommend and external reg. be installed with large heat sinks ect. and wire
Car stero and 4 wheel drive mags.have ads for this stuff
I've got some in stock