Later USAF F-4Es were modified in the early 1980s to carry the 9G F-15 600 gallon centerline fuel tank. The standard configuration became centerline only unless overseas deploying. Then all 3 tanks. This change was great along with smokeless GE J-79 engines which were more powerful and economical and tactical.
That would make sense, the F-15 tank would be a regularly stocked item to reduce inventory requirements for the older F-4's, enhancing mission capability.
I remember the F4E's being overhauled at McClellan AFB in the mid 1980's. The older engines did belch a sooty trail behind them on takeoffs, from what I remember. It was neat to walk around the various aircraft they overhauled, the F-111's, F4's, A-10's then. For a short time worked in the Industrial Engineering Flight, A-10 up close reminded me of walking around a model airplane with its Clark-Y like wing airfoil.
A little off topic but even more humorous was where I was tasked to find suitable smoking areas for employees on break. Then, the government was going to a smokeless office and shop environment (absent of the presence of flammables and substantial combustibles, of course).
Final conclusion was there were no rooms inside of any of the industrial building where smokers could smoke without affecting the non-smokers.
So, in my CAD drawing for each building footprint (done then on a second generation ComputerVision system - minicomputer based with CV's special graphics processor - a subcabinet in itself, now a simple card for a PC), the designated smoking areas was outdoors near one of the entrances.
A week or two later, the head honcho - ALC general approved (hard to remember back 36 years ago whether general or full bird).
During break time, saw older men with their gray hair smoking outdoors like high school students outside the boy's restroom. (In Hawaii, my high school hallway was the outdoor sidewalk.) Inside, I had a little chuckle over this then appearing humorous situation.