[Jerry]

Lee,

Buy an old 1960's/70's ford and get the log book with it. Put the engine number of your v8 on to the log book and change the engine size. Send it off to dvla and you will get back the log book with your engine details on it.Use this v5 as the Donor vehicle. Present this v5 to the sva tester, and he will test the emmissions as per a 1960's/70's car.( no visable smoke). Get a sva certificate when it passes. Go to your local dvla office and show them the car. They check the engine number,check the v5 and see its from the donor. Tell them that the gearbox, steering, suspension, brakes, etc are all off the donor( they wont know what individual parts of a classic car fit what car) and you get an age related plate.

Any age v5 will do the job, but bear in mind that the sva emmissions are carried out according to the donor vehicle age(pre 1975 for the visual check).
The dvla inspectors don't need to see proof that a specific part of your car actually came from your donor. When registering it you state that all the components came from the donor, and that is good enough for them.

When you have an age related plate you can put an older plate or personalised plate on.

Jerry