Everything is repairable @Nick DiSandro but its going to depend on your personal skills or the depth of your wallet, and paying someone to fix something like this would very quickly become uneconomical sadly.
The good news is for you there is probably a wealth of little wind-ups that would run on such a track, I cant speak as to Marx , although I do believe they have some smaller stuff like this
xMAAOSw53dbakiZ" target="_blank">https://www.ebay.com/itm/MARX-...0:gxMAAOSw53dbakiZ
I have a small Lines Brothers early Minic car from the 30's , made in the UK which has a 0.77" outer wheelbase so would think that would work on it lol
But I think what would possibly the most cost effective way for you to go is to actually buy ANOTHER similar toy set and use the loco on both?
example?
https://www.ebay.com/itm/Vinta...9:g:jCQAAOSwhfFbnqnX
For $70 you get another track and a train to play with
For $50 you get this one ?
https://www.ebay.com/itm/J42-V...a:g:ifEAAOSwnDZT~Kf6
However there are LOTS of small clockworks from the 30's to 60's ( and on really) that could fit the bill