I bought an 82 wagon and it has all the service records. It has had the oil changed at a dealer and it has had 20-50 put in it. Will there be any problem with this ran in it? I'm going to run 15-40 rotella thanks guys

Depends on the ambient temperature in your region. 20W50 is good for 0ºC/32ºF or higher.

I am in new mexico I didn't think 20-50 is a cj rated oil?

Some may be a CJ rated oil, but I'm not too sure. Your best bet is to do what you're already planning on doing and just use good old Rotella dino diesel oil.