I believe the tractor is an HG.  I say this because the front idlers on the tracks are the ones with the flanges on the inside of the track.  There should be a serial # tag on the side of the right hand frame rail where it meets the final drive housing.  You will want to become acquainted with Landis Zimmerman and the other people at Zimmerman Oliver- Cletrac in Ephrata, PA
His phone number is (717)738-2573.  He has lots of knowledge on these old crawlers and has parts and manuals and other things you will need for working on this crawler