Well, I've done a fair amount of research on this, and have kept my eye open whenever the subject comes up. One day I might even get around to doing it myself...
So, what I've heard:
The 5hp increase is probably overstated. Or, maybe you use nearly that much, but only at the high end of the RPM range... most of the time it's much less. So don't expect a very noticable kick in the pants increase. One thing you do gain, is less fan noise, letting you hear the mechanical music of the motor a bit clearer, and a little quieter when cruising down the hiway.
I don't remember a proper CFM number, might have been under 2000, but you need to research that. I'd think IAP and Centerline's fans would be a good starting point, if they say the capacity. Remember, they have to clear the engine, pulley, and whatever else might be in the way. Search around on the BB and elsewhere, too... Hope some discussion comes up on this, would be good to get opinions on the latest choices out there...
Amount of current... There was a thread about "what do you lose more with, the mech fan, or the electric, in alternator draw?", but I know that you wouldn't lose much with an electric. (12V X 13A=156W, 156W/768= 1/5 to 1/4HP)
Is your charging system up to 5-10 or more extra amps? That's another question. 74, you probably have the same Bosch 45A alternator that I had stock (77). I just replaced mine, due to shot brushes and commutator. Got a rebuilt 90's one, you get 70A, and an internal solid state regulator, for $81 without the core charge. (Kragen) If you have a stock setup, no massive radio, or bigger headlights, etc... I'd think the stock 45A would be OK... If not... it's probably a worthy upgrade for everything else, as well as the fans that will only come on now and then.
HTH...
Jon