alternator tech help

i was going to ask this in my other post but thought that someone else may want to know the same things about the alternator as i do...now for the crazy ??? my car is the 70 duster it has the 3 wire alternator on it already but how can i tell the amp. of the alternator???i plan to go to a electric fan/water pump drive and i have the holley fuel pump on now as well.. i dont want to run into any electric problems when i install this set-up...i do know that most of the fans that im thinking of pull about 17.5/18 amps the water pum drive i have not found that yet still looking and the fuel pump i have to get on the web page and find..i understand i may have to up grade the wire from the alternator back but is this a most????now last i have a small denso off a acura leg. but has a total of 5 wire 4 in a plug and 1 for the hot does anybody have asetup like this that could share with me about the plug thats on it...if i dont have to use this (denso) i want i would like to keep the one on it now, but if i have to i have to....sorry so long but hay have to ask the best right.....