Iv'e seen these. They are mostly used with four post ramps to allow a vehicle to be jacked up while on the ramp. Not sure if you would be able to use one with your pit as they normally run on small steel wheels and may crack the pit's gell coat when loaded, but could be a good solution if you can.
The supporting weight is 750kgs/15cwt, its made from 2 lengths of 2 inch square box section spanning 1 meter welded to a plate. I would think its capacity should be fine especially if the jack stands are near the edges.dont know the SWL of the plate for putting axle stands on , i know it depends on size of car over pit as you my not be able to put axle stand under car due to chassis due to pit size/car, so jacking beam better option as these are adjustable,,