Engine swaps / logbook / dvla

just been looking about on ebay and have seen a bike it seems legit full service history 4 keys logbook the lot, but the engine numbers dont match the logbook the frame numbers do,

is this an easy fix do i just send of the v5 with the new engine number and thats that or is there alot more hassel, he has nothing to say where engine come from but has 12 months tax mot, he has had the bike for 2 years.

 

i have checked via hpi everything clear but it doesnt show engine number

the number on logbook is 156200389690
i no thats well wrong at they start with a letter and are only 10 digits long could this be dvla fault ?

 

just change the engine number on the V5 via DVLA and thats it...sorted. As long as the enjin aint nicked theres not a prob

 

ok cheers stig no its not stolen i have phoned the police and had them check the engine