I did some more studying yesterday evening and figured out some things. Bear with me, I've never gotten into this hobby as deep as I have in the last 5 days. I don't know all of the terminology, but am quickly getting up to speed.
Believe me when I say that this thing is very, very worn out. I'd estimate there's 2-3 mm of wiggle in the rear and probably 1/2" of slop in the front. Between the axles and cheap wire tie rods, it turns sharp left in reverse when going arrow straight forward. I'm furloughed right now and looking for things to do. I've got 3 cars and 2 sewing machines scattered all over the property, a 390 engine, and a tailgate that needs repainted
My axles/drive cups are integrated units. I'm not sure if that is common nowadays, or what "standards" there are for any of this. They are bored so that a bolt come sthrough them to then nut the wheels on the outside. The wheel goes on a 6 mm hex portion of the axle, and the axle is 8 mm between here and the drive cup. There is a nylon on the end of the drive cup (very hacky, IMO, and another one behind the wheel, 6.5 mm wide...Did I mention that this thing is worn out?
I don't think that there enough meat to ream out for a 12 mm bearing, but I can feasibly turn down the 8 mm axle in my lathe to 7 mm, and fit a 7x11x3 bearing on each side of the boss in the middle of the knuckle. This would move each wheel in a minimum of 3 mm, but eliminates both nylons. There is enough wear on my axles that they are already down to about 7 mm in places anyway. The driveshafts have a ton of play in them, probably on the order of 5 mm, so I don't see an issue with them being too long/binding. The only downside I see is that the hex of the wheel registering on the round portion of the axle will be almost gone - not a big deal to me, I can figure out bushings/shims and/or buy a new nylocks. The wheels being 3 mm inboard should not interfere with anything. Short of 3d printing entire hubs/knuckles for front and rear to accept different axles, this seems like the ticket to me. I'll take pictures as I progress!
I'm looking to upgrade the springs to actual shocks, and rectify the tie rod issue. I'd also not mind putting slightly narrower tires on it, without knobbies. I think everything I've seen nowadays is a bigger hex, so I'd have to adapt something, or change axles entirely. My servo seems fine - but if it needs changed to have better tie rods, I'm game. At a minimum, I think the servo needs "wedged" into it's housing to eliminate a bit of slop in how it's mounted. If you have any ideas on what is out there for tie rods, please point me there.
I do appreciate the assistance! Once I have a couple hundred dollars sunk into this thing, I'll shelf it and start on something real.
Edit:
I see now that the servo saver that's included on the car is introducing a lot of the slop in the steering, so it's likely that this will get replaced.