Early version at left; later version at right has different wheels and a revised base (see below).
Toy size
Length
Width
- early version
- late version
Height
(incl radar dish)
98 mm
79 mm
81 mm
54 mm
3 7/8 in
3 1/8 in
3 3/16 in
2 1/8 in
The most tell-tale differences are that the Roxy copy has more and more pronounced ribs on the top cone of its body, with courser pebbling around it. But all other details are also different in dimensions/thickness to some degree.
Markings
Above left: Early Roxy version
Above right: Later Roxy version
Left: Spacex Prospector
As a final note, the later wheels fitted to the Roxy Prospector were copied from a Tamiya kit of the U87 vehicle featured in an episode of Joe90 (lower right in linked image).