Hi..
You need to request a V55/5 from DVLA to register. It takes a week or two to send out. In the meantime call Adrian Flux and get chassis only insurance (doesn't cost any extra, you just tell them the reg number when it's issued)
The next step is MOT on chassis number, you'll obviously need to trailer it there which is a pain due to its size.
Once you have the MOT and insurance you send the lot off to DVLA with the 654 (Withams are notoriously bad at passing these on and it costs £25 to get another!)
Don't worry about all the boxes on the V55/5 just do the easy ones like weight, engine size etc.
Once they see the 654 they are happy and get the V5 out within the week.
Good luck.. I've done a few of these recently and it's a pretty easy, quick process.