when building a kitcar in the UK we have a test to meet the requirements of for the car to go on the road. If I was using a chassis from an already registered car and the engine then an IVA (individual Vehicle Assesment) wouldn't be required.
So the test / manual. Its 200 odd pages of criteria to meet, from lights (angles, postions, markings), fuel tank, wiring, fixings,. To the radius of edges within the cockpit area.
I've been reading the manual over and over for the last month or two, its key to know as much as possible because you will need to build the car too meet the requirements. One for gullwing doors for instance is that the car must have a bolt with audioable warning if the car is moving and door open or an automatic way to close the door if the car starts moving.
Below is the link to the site that hosts the manual..