Montevideo(Uruguay) to Cartagena(Colombia) by rail?

I got invited to a friends house in Uruguay for January. I'm not sure if I'm going yet, but if I do, I'd like to take the train back. From what I can tell, I'd have to take the train to Montevideo, ferry to Buenos Aires, train to Posadas or Tucuman. From there, I'd have to take a bus to Peru, where I can get another train. From there, it's looking like no passenger rail service past Machu Pichu.

From Cartagena I'll get to Colon, Panama. I know of the Panama Railway to Panama City, but from there, it looks like I'm stuck with TICA bus all the way to Mexico. It looks like there might be some service in Costa Rica and El Salvador, but nothing helpful. Does anyone knows of anything?

Well itravelled in the area in the late eighties . but things have probably changed . the buses were good , so its not too bad if theres no trains .
How long are you planning to take ?

Well, the trip may be off because of college issues that just came up, but if I do still go, I'm not really all that sure. I know it will take me quite a while to get back though. I'm leaving atleast a week for that.

youll need at least a month , no way you could do it in a week .

I'd say 2 weeks if I fly from Cartagena, but yeah, a month if I go the rest of the way by land.