Yeah, I'm surprised Google yeilds nothing.... but to give you a rough, eyeball idea, a 6bt with the big fan will go from the firewall to about 2" away from the radiator in a 73-91 GM truck. Don't quote me on those 2", that's from old memory.
Actually, CrewCab has some pics up in his thread I think. And the measurements are out there, I just don't have access to my laptop right now.