Is not the sites fault that Mosler sells so many versions of the same car and then decides to send to tests versions not available anywhere.
Officialy, there were only:
5.7L 350hp (MT900)
5.7L 435hp (USDM and UK MT900S)
7.0L 505hp (German market MT900 GTR)
7.0L 530hp (USDM "new" MT900S)
7.0L 592hp (German market MT900 GTR XX)
5.7L 630hp (UK market MT900S/C)
There never was, officialy, a 550hp MT900S, but that was the only one tested of the versions with the LS7, appearing on Car and Driver and Sportauto.
There were also some test of the original 350hp preproduction version on America, and two of the 435hp version, and that's it.
PS: There have been only 2 photons build, albeit, saying that there were lots of versions of it kind of represents how the MT900 rolls, 6 different official versions (Photon is a package) and most of them have been produced only once.