When I registered my H4, in June 2000, once I understood the process I found it easy to complete.
Your car will need to be inspected by your local VRO. Depending on the VRO they may come to you, like the Chelmsford office did for me. They were happy to send someone out to inspect the car before it was 100% complete, but all that was left was some interior trim. They needed to see the car in a state that would properly represent the completed car. They looked at the parts used such as engine and suspension to check things like the chassis and engine numbers. They then looked through the supporting evidence I had proving the age of the donor car used and purchase of the kit itself. I was given a signed receipt for this documentation which was taken away.
I then decided I would MoT the car the week before the SVA to hopefully pick up on possible SVA failures, plus give the car a run. The MOT was passed first time and the certificate written out based on the chassis number.
For your reference I have a draft of the March 2004 SVA manual available for download. (You might need Acrobat Reader v6 to view this) The SVA was next and that was passed at the second attempt, only due to a stiff UJ in the steering. I believe all Quantums will pass the SVA without too many problems, but speak to the factory to check with any problem areas they know of. For the H4 they can provide you with a letter proving that the side windows are toughened glass as the markings from the donor windows are hidden - this saves taking off the inner door panels to reveal the markings.
Armed with my MAC, MoT and receipt/case number from the VRO man I went to the VRO office where they pulled my file which already had an age related plate assigned to it, so the registration was quite quick. The final task was a trip to Halfords to get the plates made up. I believe now you would require documental proof before you allowed to buy number plates, which you should have been given by the VRO.
All Quantums should be able to retain the donor age related registration plate as they comply to the guidelines listed under section D on the DVLA site. A tip if you are changing the engine is to register the new engine number with the donor car before you start registering your Quantum.
Much of the above will be useful for general kit car builders too., although this was written about registering a kit car in Jone 2000, so some of the above may be slightly different now.