shoeless,
What year truck do you have?
I believe in simplicity, so I suggest a one-wire GM alternator (it has an internal voltage regulator). The major disadvantage of the one-wire alternator is that it does not start current flow until your engine reaches between 900-1200 rpm. After that point, the alternator produces current at all rpms. This has never been a problem for me because my engine usually starts with a fast idle, and thus the alternator starts charging within seconds of starting.
The main question would be the output rating of the alternator. I think the lowest rated alternator is 35 amperes (12v) and the stock 1/2 ton 6v generator was around 25 amperes (6v). If you want a powerful stereo system and plan on adding a lot of accessories, you might want a more powerful alternator.
Search the "Electrical Bay" forum on this site for "alternator" and read all the threads. There is a a lot of good advice there.
There are a variety of methods for attaching the alternator - the lower bracket is trickier than the upper arm (you might get away with your generator upper arm). I bought an alternator bracket and alternator from the same vendor and still had to drill and grind the bracket for a good fit.
By the way, JC Whitney has one-wire alternators at good prices.
Good luck,
Tim
