Here's an old picture of my F7 & FP7 while still being detailed some years ago. I took it to show the difference in lengths, the FP7 being longer by 4ft.
The conversion from F9 to F7 mainly involved removing the set of bodyside louvres that were forward of the porthole, filling in that existing forward porthole and drilling a new one closer to the cab, and making a frame for the porthole from suitable plasticard.
The splicing of two F9 shells to make the FP7 was done by someone unknown, as I just bought the model off Ebay, and even the seller didn't list it as anything other than an Atlas F9. The builder actually spliced the bodyside panels together rather than just a vertical cut down each body - it's such a neat job the only way to see the joins is looking inside the shell when it's off the chassis - which was also lengthened of course.
I added all the detail such as wire handrails and grab irons, winterisation hatches over the rearmost roof fans, scratchbuilt spark arrestor exhausts, warning beacons, windshield wipers, firecracker aerials, roof panel lifting eyes, sunshades over cab side windows, etc, and painted & decaled them myself.
I finished 502A as it was in the late '60s/early '70s, still with a top headlight, and not too dirty.
2203A was finished as it was late '70s, just prior to withdrawal in 1980; rather grubby and work stained, top headlight plated over, replacement orange number box on the Engineer's side of the nose (off a Milwaukee F-Unit, perhaps?) plus of course the trademark masking tape 'draft proofing'!!