Snappy V2.0: Land of confusion.

[Mooselake]

Back to the original topic, pretty much any common 3D printer stepper that fits will work. Given a choice I'd use a Kysan 1124090 (quiet, reliable, lots of torque) but you may have a space issue (my also non-functional 1^ parts collection is two floors up or I'd check). From a quick look the Wantai you list should work.

You want a motor voltage that's less than 12V (the driver current setting will protect it), and less than 2A, around 1.5A is better, for most 3D printer driver boards including RAMPS, and most likely 200 steps/rev. A 400 step/rev motor will work, but I'd back off to 8 microsteps on the driver.

You configure the motor by setting the current limit on the RAMPS board (you can do it empirically, up the current until it hits the 5 second limit (you can hold your finger on it for 5 seconds without having a high pain tolerance) then back it off a little bit). Steppers are designed to run at higher than you might think temperatures, despite the urban legends running pretty darn warm won't hurt them. For a standard 200 steps/rev motor at the standard 16 microsteps/step the calibration will be the same regardless of who made it, if you run across a 400 step/rev motor then either set the driver for 8 microsteps/step to get the same results, or double it if you stay at 16. Since microsteps are notoriously inaccurate, think as much as +/- 20%, you're fooling yourself if you think more tiny steps somehow magically make it better. Actually motor steps can have pretty high tolerances too. Since you set the current with a tiny screwdriver, and if you use a motor/microstep setting that matches the stock motors (200 and 16, or 3200 steps/rev) you can use the stock firmware without any changes.

You might be able to trace/cut/sand to fit your missing MDF pieces out of MDF, hardboard, or something similar since you seem to have an example.

Aviation club? Way back when, in the early 80s, we bought a Quickie Aircraft Q2 kit and got it about a quarter assembled over a couple years of evenings and weekends. We then moved (back to a farm the bank and I owned in the north woods) where I didn't have a good place to work on it, had 3 daughters, plus a high-travel time job and a high workload small farm, and the semi-completed kit has been sitting in several outbuildings for around 35 years now. Like most homebuilts it'll likely never get completed I'd like to build a power chute, these days going nowhere slowly would be a lot more run. 200 hr PP but haven't flown since the wife/mortgage/kids/etc thing kicked in, it was a lot easier when I owned a trailer on a small airport and kept it there rent-free in exchange for night watchman, minor mowing duties, and paying a $6/month hanger light bill.