if you can get the original sale from ebay you should be able to get your bits back
the bill of sale for the car though, thats the tricky one, if you've still got the recipt then you shold be fine, if you ain't they might have plenty of time on their hands taking bits to peices to work otu what is and isn't yours

as soeone mentinoed, if you do get it back you may have to Q plate it

my mate had the same thing ages ago when he bought a cavalier
went to the car auction, couldn't find what he wanted, guy by the door said "buy this, cheaper than in there, job jobbed" so he handed over £3k and off he went
when he came round to see me with his new car i said "but if it's a 1.8 why has it got a 1.6 engine in it? why is there no ignition lock? the numbers on the windows are different to the reg plate, etc etc"
2 weeks later dibble came and took the car and he got sod all