Academy/Minicraft Models has a series of small, simple box scale model aircraft kits. One of the planes in the series is the 1/480 scale C-5A Galaxy Transport. There's an in box preview at Modeling Madness. There's not much to the kit, but it's nicely molded and fits together well.
I like the design and engine placement of the Boeing YC-14 and the Antonov AN-72 & An-74, which use the engine exhaust flowing over the upper wing to aid in STOL. I have a 1/288 scale kit of the An-74, made by Eastern Express, and its engines are about the same size as the engines on the 1/480 C-5A. That's when the idea struck me to make a US version of the An-74.
Putting four engines on top of the C-5A's wing and calling it a day was not particularly interesting; the kit's odd scale wouldn't fit with any other models I had, and it just didn't seem like a very creative modification.
Instead, I rescaled it to 1/350 (just by saying that "it's in 1/350 scale"), I made the fuselage shorter by cutting out a couple of inches ahead and behind the wing. I also modified the top of the forward fuselage. These modifications gave it a stouter appearance; more like a C-130 or C-17.
The kit is designed as an in-flight desktop model, so no landing gear was included. I made openings for a nose and main gear and scratchbuilt the landing gear.
The engines are based on the Eastern Express An-74 engines. I lengthened them and modified the exhaust. I made four copies of the modified engine and faired them into position in the wing's leading edge.
The kit decals were somewhat off register and the cockpit window decals were too small, so I made new decals and printed them on my ALPS 5000, including new window placements for the cockpit windows.

The backstory for this design is that the USAF was looking for a STOL cargo plane, similar to a C-17 or C-141 but capable of delivering cargo and personnel to unimproved and very short runways. This model has a wingspan of about 49.5 (scale) meters (162 feet) so it matches the wingspan of the C-17 and C-141.
The figure is from the 1/400 scale Preiser passenger and aircrew set (Preiser 89400 Google search). They're actually not far off from 1/350 scale (or at least it's very hard to tell the difference.)
This isn't my best effort, but it was a fun build. The exhaust staining is a bit excessive, especially considering that there's little weathering on the rest of the plane but I like the overall result.