Hello Greg
My 2 cents worth is if you can lift the dolly ( nice design too! ) onto some " pucks " that would work.
The puck could be machined from aluminum with a dimple on the base that could fit into a hole drilled into your slab and on the top a machined recess that the dolly legs for fit into.
Second suggestion is if you mounted a laser on the dolly, ( if you didn't want to mount your existing laser bunnings have on for $50.00
https://www.bunnings.com.au/bosch-pl...laser_p5660477 )
that would do the trick.
If it was mounted on one of the legs and when the mount was aligned you marked a point on a wall where the laser shone that would give you an easily repeatable reference point - the furthest you can mark the laser point from the dolly the more accurate it will be.
Hope this helps.
Ed