I done the some decimeter<->centimeter fumble in my previous ramblings.
But I was estimating into round number to some degree too.

Looking it over, you are right, the tank will be 66.2 quants etc.
But damn, its a bit under the 3DGS standard of 80 quants being a collision "hull".
We may need to rescale if our bullet/shell collisions start to fail at close range(hi-speed).
But as youve seen, its not that hard at this early stage.

And in a pinch, we could also re-scale any models in-game, like we are doing with the terrain.
Its the in-game quants that are the important ones when it comes to collision hulls.