Adjustment - 10k or 5k ohm linear potentiometer.

Trim - 2.5k, 1k or 500 ohm linear potentiometer.

I've used three different types of 10k ohm potentiometers successfully for adjustment. On the throttle channel, 10k works very well and I'm able to turn it down low enough that my cars barely move. For steering, I'd use 5k since going straight isn't very useful. I've also only used single turn potentiometers, but a multi turn might be interesting. Most recently, 3310C-101-103L-ND because it has a small shaft and I hoped to put a knob on it. Previous to that, 987-1279-ND because it has a nice big shaft that just acts as the knob. I also used 987-1382-ND (which has detents) with the idea of having the main shaft act as throttle dual rates and the secondary shaft act as steering dual rates. But steering dual rates weren't important enough to bother with, so I never used the secondary shaft. Of these three, I prefer the first for the small size and the second for looking good and being easy to use. I wouldn't bother with the third. Any linear 10k or 5k ohm potentiometer will work, feel free to browse Digi-Key or your favorite electronics supplier and find the best one for your application. Go to town with Digi-Key's Rotary Potentiometers - Linear section, but be sure to filter the list down to only the values you want... and even then, the list is overwhelming.

For the trim potentiometer, I've tried 10k and 5k ohm so far and they're too much and it ends up being extremely sensitive. The problem with both 10k and 5k is that the range used is probably 1/10th of the total range so adjustment is very finicky. But I don't have anymore transmitters to modify, so I'm not sure what would be perfect. If I were you, I'd take a risk and order a 1k and 500 ohm potentiometer instead. And of course, the original article even suggests a 1k ohm trim potentiometer. Here I've also only used single turn devices, but a multi turn would probably be perfect for this application due to the higher precision. Most recently, I got 3386F-502TLF-ND because it has a nice, easy to turn knob. But this is a 5k trim pot, I only recommend the style. I would probably get 3386P-102TLF-ND, a 1k or 3386F-1-501TLF-ND, a 500 ohm potentiometer. At Digi-Key look in their Trimmer Potentiometers section and make judicious use of their filters to only show what you need.

You'll also need wire, shrink wrap, a soldering iron, screw drivers, scissors, and who knows what other tools.