That certainly is a gravel kit. I looked after a 737 based on a gravel strip for a few summers, it was a great time.
From what I remember the differences between it and the regular 737-200s in the fleet were (it was also a combi, but that's its own can of fish)...
- The "ski" on the nose gear, basically a big board mounted to the nose gear that went around and behind the wheels and kept gravel from being flung up and beating up the underside of the fuselage and going in the engines.
- The only times I really swore at it was trying to work in the avionics bay, the ski had a big no step placard and it could not have been more in the way for getting in and out of the avionics bay.
- Changing nose wheels was a bit more of a chore too. What I remember working was a bottle jack with the longest extension amount you could find to get the thing way in the air, and then there was a pin you could pull and have a rampie with a young back to lift the back of the ski and hold it there as that would pivot it such that the front end was low enough you could just wiggle the tire past.
- Other than that it actually worked pretty well.
- The nose gear doors were quite different and smaller than a normal 737 and there was a ridge added around the edge of the nose wheel well to fit the ski.
- When the gear was retracted the ski actually became a nose gear door, the small doors just covered the areas the ski didn't and the lumpy ridge was to fair the ski in with the surrounding fuselage.
- I remember the ski had a bunch of big springs and a little hydraulic setup to make it sit right on the ground and then align with the fuselage when retracted. When extending and retracting the gear sitting in the cockpit you sure knew the nose gear was working because during the cycle there was a moment where the ski would be almost vertical, which was basically a sheet of plywood in the airflow.
- The lower antennai had a fancy tape that went on the leading edge to help gravel bounce off. Seemed to work, I think the ski caught most of it anyway.
- The lower beacon light had a fancy little rock guard sitting in front of it. Usually worked, but I did keep a beacon lense in my little saved the day again bin though.
- Main gear were mostly stock, save for an extra plate on the lower front to help protect some of the hydraulic lines a bit, and a little rubber mud flap that hung out behind the tires.
- Overall the gravel kit worked good, but you did change main wheels a lot more often than is normal because the tires would regularly have cuts and gouges in the tread that were beyond the limits in Boeing's maintenance manual. If I was down to one spare main wheel left on hand there was phone calls to get some more on the next flight through. We got good at nascar style main wheel changes on that airplane.
- Inboard trailing edge flaps had a fancy rubberized paint on the lower face as they would get a pretty good beating some days. The fancy paint seemed to bounce off most of the rocks though, every now and again we'd have to do a small repair but usually nothing major.
- The engines had a vortex dissipator mounted in the bottom of the inlet cowl
- This thing had two jobs: first was to disrupt the little vortex that would otherwise form and suck up gravel, and second was to put a dent in the FO's leg every morning.
- Simple system, it was just a pipe from the 13th (I think, might be wrong) bleed air duct on the engine that came down and sprayed air in a fixed pattern, with an on/off valve in the duct wired to a switch on the overhead panel in the cockpit, a pressure regulator, and I believe a pressure sensor going to an indication light in the cockpit.
- Worked good, front fan gets an extra good look at on the walk around just in case but I don't remember having any real fights with it.
- The airplane did get dirty a lot, basically any time there was the slightest bit of moisture at any point during the day we were washing the airplane that night. Those thrust reversers would pick up the mud and sling it all over everywhere.