Revell provides reasonably correct panel line detail on the body, though it is raised and the lines are huge. I sanded off all of the panel lines and re-scribed using my trusty Tamiya scriber. This comparison picture shows what a difference the new panel lines make. After I re-scribed everything, I fixed up the door on the left, removed and corrected the door on the other side, and added lots of little details. The rectangular vent thingies littering the sides are from the Tamiya Flakvierling. It only comes with 4 so I made a mold and cast tons of them, they'll be all over every model I build from here on out! The "stairs" going up the sides were cut from L shaped Evergreen Styrene stock, using a jig to get them the same length and align them on the model.
I spent about a week scratchbuilding the details on the top rear cutout, from mostly sheet styrene, but I'm really pleased with how it turned out. It's very accurate to the original model. The Flakvierling part on top of the body was scratchbuilt before I got my hands on the Tamiya kit, but it came out surprisingly close to the Tamiya part. The large vents on the top/front are cut from vent parts from an old tank kit. Rather than trying to cut perfect holes for them in the AT-AT kit plastic I cut out the whole section and replaced with styrene sheet for better precision and appropriate depth.
It's apparent on photos of the stop motion studio model that the front and back side armor sections had some kind of rough texture applied, most likely to evoke the feel of cast metal parts you sometimes see on WWII tanks. Texture and sheen variations are something that I think most modelers neglect, while they're often the focus when doing 3d models, so I definitely wanted to recreate this on my model. I stippled on Mr. Surfacer 500 with an old brush and came up with a pretty good texture.
The neck was a real puzzle, though made somewhat simpler by my decision not to articulate the model. After trying a slinky that was the right size but not "ribby" enough I came up with a good solution. I wrapped fishing line around a pill bottle of appropriate diameter (seen here with the kit neck), glueing with CA as I went. A slice of PVC tube was glued to this, to be inserted into a hole cut into the body. The framing was made from sheet styrene, and I spent 3 days making the round joint greebles as accurate as I could at that small size.
Greeblie nurnie heaven! The underside engine area is full of tasty details on the studio model, so I went to town here. I was able to find some matching pieces on the Flakvierling, and scratchbuilt and kitbashed a bunch more to emulate the details on the studio model. The attachment points for the cylindrical engine parts were innacurate, so I filled in the big one toward the rear with bondo. I also cut out the opening at the rear for a detailed housing piece that's completely missing from Revell's molds, and scratchbuilt the engine block that fills the space. The mounts for the hip pieces were scratchbuilt from various tubes and cast in resin, so as on the studio model the legs don't actually attach to the engine cylinder parts at all.
Here are the cylindrical engine parts and belly after a coat of Tamiya primer. I believe these were made from Harrier parts on the studio model. (side note: the Jawa Sandcrawler uses these same parts for it's engine detail on the back). The kit parts are decent, but missing the large vents on the sizes of the long one and the cutaway where the legs attach on both. This little greeble at the front of the cylinder block was actually easier to build than I had thought. A bunch of thin slices for the spokes and I sanded the assembled bit to get the outward bevel.
More pics. The harrier vents on the sides are epoxy putty with textured styrene for the actual vent surface. There's a fair amount of scribing and greebling on these engine parts.
The back cylinder is missing the "lampshade" housing at the rear (where do I come up with these descriptions?). I build this from a crescent of sheet styrene, scribed and bent into shape. There's also some detail in the opening into the center of the cylinder, which you can't really see after assembly but I built it anyway.