Transmission oil and very fine steel wool 000 to get rid of all the surface rust. You can reblue or leave as is .... be careful using the steel wool - just hit the rusty pitted areas. Do all the details ...
This is a nice piece, was customized anyways. Once cleaned up consider reblueing, would be worth it to me. It was a really nice piece, too bad was left out to the elements.... it is worth it to make it nice again... I have a similar in 32-20 love it.