Welcome to the forum. It`s nice to see you made it on to here.
There is another 126 member in Colchester

In the original photos it had the early wheels/hubs fitted, which were the same stud pattern as the classic 500s. I`m assuming it would have also been fitted with a 600cc engine and was based on an early donor car.
Looks like someone has modified it later on in it`s life?
Maybe it would be worth rubbing a bit of paint down to see if it is blue underneath.
Your car could be the first one ever built if it`s the same car as in the pictures. The car in the pictures was a demo car. The chassis number also indicates this.
My friends car is number 000404 which makes it number 4.
The one I`ve got is a later convertible version which is numbered completely different.
The FZD is the preferred choice when tuning these engines. Rusty`s Uncle on the forum is your man if you go down this route.
Looking forward to the updates on this.