Actually, I replaced the stock jack with a Walker hydraulic that I keep under the left side of the seat frame, but would have made a bracket for the stock jack by the pillar. That is where later models located the jack if I'm not mistaken. I used the space by the pillar for a fire extinguisher...
My '77 had the same setup, but I found moving the jack to the newer jack storage location by the pillar more useful, as it left the full underseat area to store my toolboxes.