Two quick updates: 


I've bought this 749 RS frame and found that it has no frame number (and never had - it has no machine marks). This has lead me down some interesting paths.


Apparently, Corse personnel go to the factory and ask the production frame number man to reserve a number of frame numbers. These are usually consecutive and are in exactly the same format - produced on the same machine - as road bikes. 998RS and earlier frames were stamped and 999RS stickered.


We think 998RS frames were not produced by Pierobon, but by Verlicchi. This has to confirmed and it will be interesting to see if the welds are similar to the 749-RS frame or have the model designation on the headstock.