It looks identical to my SB465, apart from the knobs. Lovely slab of ebony and the top is probably Paduak.
I suspect Jack is right and the electrics have been replaced. This is not necessarily a bad thing, the pre-amp in mine died (not uncommon) and there's a certain home-made nature to some of the soldering. I think £400 is a bit high too, start at £300 and work up :-)