I’ll start by saying “back in the good old days”, to get an unregistered car or motorcycle back on the road, it was simply a matter of taking a few details down to your local post office and registering it, paying a small fee, getting some new number plates (if you didn’t have the old ones), and walking out.
I did this on many occasions back in the 1960s and 1970s, usually with either Austin Sevens or Morris Eights. One such exercise in the early 1970s involved a 1936 Morris Eight four-door