bevel set interchangeability?

[Ed Levin]

I'm considering changing the final drive ratio on my S1 5-speed (818.540 'piggyback') gearbox.

The parts catalogue lists part numbers for different bevel sets for the S1 4-speed gearbox--with various ratios for the various S1 berlinas and coupes. For the 1,6HF, with the piggyback 5-speed box, the catalogue lists the exact same ratios with different bevel set part numbers (all with an 818.540 suffix).

Here's the question: Are the 818.540 bevel sets different (longer pinion or something else?)? Or are these exactly the same parts and they were simply given alternate 818.540 parts numbers to homologate them for competition?

I already have all the guessing and speculation I can use. Does anyone actually know whether, to take one example, the 11/43 bevel set listed for a Coupe 1.2 (1204128 818.000) is really the exact same part as the 11/43 bevel set listed for the 1.6HF (1290374 818.540)?

Thanks.