Your question asked 'what is this?', not 'who built it?!' but it was made by John Nash in Kent, South East England, with JNS standing for John Nash Special.
I didn't mean you were wrong, far from the truth, incomplete or just close...I had it filed under 'Nash' and
my memory told me it was a Special built by John Nash. Your answer was full of details but was missing of the only bit I had in that moment, the builder's name
There were too many matching points and the lock was there just to let you give me the name I needed to be sure:
I have an article written by Nash and it's called just Monoposto ('home maid' !) and another long description of it from a website where it was proposed for sale, calls it just 'Alfa Tribute'. Now I can be sure we are talking of the same car
