It appears that the oil tank is under the seat hump, early Yamaha roadrace style... I'd asked a couple years ago if the stock CB750 pump would support this kind of arrangement but I don't think I ever got a final answer.
Uncrash, what pic were you trying to post? Hopefully it will help with the gray textured question. If so, could you please repost? I've been looking for an answer since I first saw these photos. RR