Sokkia Radian IS/GSR2600 Serial Commands and Manual

Hello all, I've got an older RTK setup that consists of a Sokkia Radian IS rover and GSR2600 base along with some PDL radios. I'd like to use either of these units, or both as a system again, for a hobby project.

I remember years ago when we first got this system I was able to get 5Hz NMEA output from one of the units by issuing some commands manually over the serial interface. I can't seem to find any references to the serial interface other than what's described in the operations manual (PDF) which I found online.

I know it's a long shot, but if anyone has a copy of the "Radian IS/GSR2600 Advanced Reference Materials", or any technical documentation I would certainly appreciate it.