I have made these adjustable stands long time ago before fifteen years.
It's a very simple construction and easy to made with no special tools and only from scrap.
The needed materials, dimensions and descriptions are in to the photos.
Here are some photos with the stands at use. Also can used to lifting a caravan or car.
Unfortunately I haven't more photos.
Personally I had made it for my caravan but I can't remember or count at how many different works I have used all these years.