[rich]

Lets see if I've got this right!

Cheetah Viper's were made by cheetah cars run by Kevin Mason between 1984 and 1986, these cars were not well received by the press and so only eight were thought to have been made, these cars had the smaller arches, the larger arches were first added to a Granada based Sheldonhurst in early '85 which later became Brightwheel in late '85.
In '86 the first Jag based Brightwheel Viper was marketed.

So would a Cheetah have been Jag based?
The ad says 'Cobretti chassis' and 'fibreglass body shell' is it possible that its not the intended shell, its hard to see from the small pics but it seems that the doors are fitted and lights holes cut out, may be second hand possibly damaged/repaired.