On the Opel Speedster the build number is embossed on the alu dash bulk head.
I'm pretty sure that the Opels have consecutive numbers on their dashes even though there were some VXs built on the line inbetween. For example, whilst my Speedy was number 0811, I think it was build number 1085-ish. So I think in this case, the Speedster number is 4045, but the build number is 5128.
Sounds reasonable
