This one's a conventional Mar-Lift dolly.
Except it is no longer 'conventional'... I cut the side tubes and inserted 7' of thick walled pipe of which the OD is smaller than the ID of the Mar-Lift dolly. They're pinned with through-bolts to keep them from turning or slipping out.
The purpose for this mod was to get the top tube of the lift behind the sled so it could go all the way down to the ground if you wanted it to... For even more height! The stock configuration provided minimal height because the top tube would contact the seat, and you had no more lift!
So there I go, always tinkering & modifying stuff...
The 25L 6US Gal. pail of tranny fluid gives you some perception how far off the ground the track is. If I ever need to install studs, or tinker with something back there, It's the right height to pull up a chair, which is easier on my blown knees than squatting.