The plastic gears will be fine as long as they seems fine and not worn out.Sounds like a strong engine you got there,so the plastic gears might become to weak and break after a while.I dont have so many parts,its just the wisbone i can think of right now.It was more like an example to which parts that can be used,even if its a bit worn out.
Glad to hear that youre out of the wheelchair,must be strange to learn how to walk again.A situation i can be without,but time will show.As you say,one never knows...
Have a look [link=http://www.minicars.se/sprangskisser.htm#fg]in this link[/link] and see if theres any parts you can use that is compatible with your car