99 to 02 are fine, if you go lower than that they will probably be LT1 fans which arent really that diffrent.
good luck.
Daniel

 

you don't have to upgrade your alternator, unless you have alot of high drain equip on your truck. the fans work off your battery [which i upgraded to optima] they do not run all the time [except in hot weather at low speed] so it is not a constant drain. my alternator has no trouble keeping up with the fans, amp, lights etc.

 

I run the huge Lincoln Mark VIII fan on mine and it works great. They are about $200 new and can be had on Ebay, used for about $100.