I'm about to do the same. Git all the info off a cummins forum. I have a huge gap between my intercooler and ac condenser/radiator. Leaving my stock fan on the inside and mounting push electric fans on the outside. They'll need to be thin enough to fit behind your grill......that's my biggest obstruction so far

outside
 

i just think they will obstruct so much "cool" air from hitting the front..... same reason i dont like billet grills with extra thin slits... its like putting your return air duct for you home A/C in a 10'x10' bedroom.... itll strain so hard to get air that you cant even close the bedroom door!

You could always modify the grill.... alot of that plastic can be "shaved" if you need an inch or so