Hi MX250
The are called Computrack.
They are used by just about every top road race team world wide to enable accurate chassis setup in the workshop. Also they are used by companies producing alternate chassis parts [such as rear suspension linkages] as you can measure a chassis in 3 dimensions and plot geometry changes during use. A really clever device - I don't who makes them now. But they are certainly still out there.
I think you could probably Google 'Computrack' and find some info. A search for a 'Chassis Dyno' will lead you astray - as they are for measuring engine torque [and subsequently - horsepower] and aren't really anything to do with the bikes actual chassis.
It would be scary to measure a VMX bike and realise just how out of alignment most of them probably are - just like the riders really.
VMX42