With a few simple mods a scissor jack can be stable enough for lifting and working on bikes.
Mods start with adding a few steel plates.
Lifting a 380lb XT600 requires a strong drill, pictured is a tripple reduction heavy duty ½" model.
1/2" x 11" x 7" Rubber Protector Pad.
A ¼" x 10" x 10" hinged steel plate locks the jack in the raised position and add's stability.
Update: Had to make some changes to the liftjack to make it more stable.
Removed the rubber protector pad, the main problem with the instability is the excessive movement of the XTs rubber mounted skid plate along with the small contact point it has on the liftjack, only 4"
A wider contact point sitting directly on the bikes frame is a much more stable safer set up
Rear tab of the left side lift plate is positioned (hidden) behind the kickstand mount while the front tab rises up to catch the frames swingarm gusset plate, this locks the frame in place with no side movement but allows the frame to pivot when lifting/lowering the front wheel
With the main jack now dedicated to lifting the rear of the bike another way of lifting the front end became necessary, similar to lifting a heavy streetbike on it's center stand, a small jack works well.
The swivel on a scissor jack is a perfect fit for the hole at the base of the frames downtube.
This hole in the frames front downtube becomes the front lifting point, being careful to avoid damaging the oil line.