We made home made jacks using inexpensive Harbor Frt straight jacks. We made a 18" square floor plate of 1" plywood and used hose clamps and 45 degree members made of conduit pipe. Works great!
I took a piece of 2x6" about 8" long, and used a hole saw to cut a pocket in it that would fit over the jack ram----only 1/4" or so deep-----to keep the board from slipping off the ram.
I span the two spars with the 2x6 blocks, locate the ram under the rear spar.
I slid some scrap alum strips between the skin, and the spar so I would not dent the skin.