The Audio Research Database has most of the information you want. It has big heavy transformers so it weighs a lot.
I have a D-79 (first all-tube version with no letter designation) supposedly tweaked by Bill Johnson himself for an Audio show at the time. It was my Father's amp, and he truly loved ARC gear, and owned it since the company started producing equipment in the early 70's (he first bought an SP-3A preamp and had bi-amped Dual 51 and Dual 75 driving Magneplanar Tympani I). These D-79's are truly special amps and they don't make anything like this any more. I believe they were a statement amp for the time. The last time I used it was with my Magnepan MG 1.6's and to this day I believe it is one of the best sounding amps I have ever heard (and I have owned a few through the years). They are way overkill in their design and I believe they only ever made a handful. Anyway I believe you have a special and rare amp, and one of the few. Good luck.