LOL! This is indeed "a very unique machine", as the vendor writes. But not because it's some rare prototype but because it looks like it's been ripped apart (notice the missing chips and the damaged capacitor) and then placed into the wrong case.
Also the C103088 motherboard revision is neither particularly rare nor is it very early like the vendor claims. You can clearly see from the date code of the PCB and the components that it was manufactured in 1988, 3 years into the production of the ST.
EDIT: It's an STF though, so 1988 is about two years into its production.
I'm sensing a business model here: Buy cheap STs on eBay (don't have to be working), rip them apart, exchange cases among each other, sell them as "ULTRA RARE PROTOTYPE!!!".