When my Z3 was put back on the road I contacted the people at DVLA. They seemed to be a competent department, covering a small area of vehicles.
I asked them to title the make of my body conversion as a BMW Tribute 275GTB. They accepted this and gave this as the whole make, rather than title and type. So nothing appears in the type or model spaces. Finally they changed the convertible to coupe at my request.
It will be worth your while ringing them up to get details of what you could title your car. I provided a receipt from Tribute and some photos. Chris was knowledgeable and helpful.
See page 16 of my thread
Scan p2 V5C GTB part.jpg