Slim fan recommended that clears mezier ele water pump
Need a fan that will clear pkz help
Motor is a 550hp 408 street strip car that radiator is a champion
I have to agree with the post about pulling that pump and going with more conventional cooling methods (really, save yourself the trouble now)
Ok, now that we got that out of the way. :D
You'll probably have to end up using twin fans if you are dead set on electric, because I have NEVER seen anything capable of cooling a big block that was only 2.5 inches thick.
Two fans would give you a spot between them for that 2.5 clearance you have, and consider that you are going to need a shroud also.
Then, that kind of a shroud will almost assuredly block to much air at road speeds unless the fans are BIG so the volume needed at speed can get through the radiator and out the back in a hurry.
Take it or leave it, but a lot of us have been there.