The relevant rule mentions components available in 1984.
There is no requirement for specific part numbered model identification
By the look of the carbies in the various photos they are die cast production parts, unlike the big black round slide mixers fitted on earlier HRC motocrossers.
GCR 16.15.13.1. Acceptable for Pre 85 class are machines and COMPONENTS built up to and including the 1984 model.
Correct.
The production 1985+ Keihin PJ was not available as a 1984 model part, therefore it is ineligible for Pre-85 racing.
The works 1984 Keihin flatslide is OK for Pre-85.
The production 1984 Mikuni flatslides are OK for Pre-85 (even on bikes that came with roundslides).
But there is a clear, visible difference between the 1984 works Keihin and the 1985+ production Keihin, which instantly excludes the 1985+ PJ.
It may be possible to submit a request to MA to allow the later production PJ to be accepted on the basis that it is operationally identical and visually very similar to the 84 works part. To give it a fighting chance of success, you'd want to have all the technical data of both works and production carbs, clearly and officially showing that the only difference is the fuel intake pipe.
But that different fuel intake pipe makes it obvious that the works and production carbs are NOT the same as each other.
