Thanks expat. The only 2 differences I could find in the 3-tank and the 2-tank versions is that the 3-tank version has the forward nose gear door with the twin square taxi lights and no signal lights typical of Air Force RF-4Cs, where the Marine RF-Bs typically have the single round taxi light and three colored signal lights on that gear door.
The 3-tank version also has the J-79-8 early afterburners which were typical of all early production RF-4Bs and Cs. Most late production RF-4s (the last 3 or 4 I think) were fitted with the thick wings and "fat" wheels of the "J" and the upgraded -10 engines and afterburner. A few earlier Bs had engine upgrades.
I'd like to find an example of a real Marine RF-4B with the Air Force style nose door configuration to be able to utilize the different "tank only" models avaialble.
I agree with you in wishing there was a true "CAP" configuration for B's and Js with tanks and missles but I haven't found one yet.
Cheers,
Steve