Missing Seat Lock Cylinder

Okay, just bought an '81 KZ750 as a project bike. The seat lock cylinder is missing so I can't change out the battery.
Anyone have any idea how to get the seat open?

Two thoughts, first, if just key cyl is missing, that cyl enagaged originally w/ either a slot or two nobs at rear of reciever. if either exist, try to rotate. if none, pull rh side cover, locate seat pivot pins and remove. as with all, the 1st rule of the Hipporaratic oath applies. "do no harm" or at least as little as possble. Luck G

Thanks gane, giving it a try today.