You may be right Borgforever. There is a "gap" in my memory there. I do DISTINCTLY remember seeing glimpses of him with that ALL BLACK frame around 1982. You may be right, because I also was under the impression that he basically had Donnay at his disposal, and they were crafting his next frame, and heading towards perhaps a high percentage graphite frame (composite with fiberglass perhaps, who knows what the end result would be??)
That frame at AKAI could very well be that larger head Donnay Frame, with more graphite that you describe. That racquet shift (almost a gateway frame between a small wood racquet to say the first Wilson Pro Staff in about 1985 or so) would certainly be enough to produce more power/ease of hitting (slightly larger sweet spot), especially if that was coupled with some more strength training. I will say this, even though he was listed at 5' 11" and just 160, that guy was STRONG and lean. People underestimate the strength he possessed, not just in the legs, but his "core strength" and arm/wrist strength as well.
Bjorn Borg defied analysis. No one could manufacture a man that won 6 French Open and 5 straight Wimbledon titles. - Andrew Longmore