If you are the keeper and you have the right to sell the vehicle, there should not be too much of a problem with the sale. On the SORN issue, in theory they could come at you for some back tax but whether this happens would very much depend on the precise circumstances of the vehicle, who the registered keeper was and why the SORN was not operated. There may be no liability at all, they may agree to forget about it or the outcome might be subject to negotiation.

In the first instance, providing you have good title to the bike, I would permit the DVLA to issue the log book and see what happens from there.