Tektronix 31 with cogo package-searching for info

[ls41028]

I couldn't pass up this little gem in the silent auction at the Professional Land Surveyors of Oregon conference this week. Anyone have any info on it? It appears to be a Tektronix 31, although the plate on the back says model 1. It seems to have a cogo package apparently made by K&E. Looks like parallel ports on the back were added on too, I'm not sure. Anyone have a manual for it or any other info?