Over the Summer I was lucky enough to pick up this Space Bird 3 variation. Space Bird by YT of Japan is a clone of Project SWORD's Probe Force 3 and as far I know this brings the total number of Space Bird variants to four. The other three are featured below. The main two colour types are grey or white. All the other variations are differences in the colour of the cockpit and engine windows and the rear engines themselves. This new combination, pictured above, is green cockpit, red engine woindow and yellow rear engines. There could well be many more colour combinations as yet undiscovered.
There may also be box differences between the grey and white types, but I can't be certain as I don't own a white one. Looking at the pictures here they do apear to have different top box art.