C d M, What a classy example, it makes the best the big makers did look poor at best. And Bianchi were very heavy.
The fortunate racer who had this bike probably needed mudguards for training.
I last rode my P/R gear in an open road race in 1956. I had 14 - 24 with 48 x 51 on the front. No problem with the chain length in exreme gears, and used a Campagnolo H/B control to allow undoing the wheel, but pedalling forward to change the front. There is a neat adjustible cam and ratchet to move the wheel slightly forward as the QR tightens, to make sure the chain is not tight. The real problem with these and "Osgears" was the chain runs much better if fed onto the cogs in line. (apart from the obvious)
I could be wrong, but the front hub might have the alternate countersinks for the spoke holes, which were intended to suppport the bend, not hide the spoke head. European wheels were mostly built with the inside spokes in opposite directions, in this case it may be that the angle and stagger did not allow this.
While I agree that the workmanship of this frame is superlative, I have also owned a number of Bianchi bikes that were also of very high production quality. Most were indeed heavier than this bike, but not all. In particular I have a Bianchi Folgore from 1941 that was built with Mannesmann Extra tubing, which long held the primacy as the lightest bicycle tubing available in Italy.
As regards the countersinking of the spoke holes in the hub flanges, they are identical for all, so there is no specified building pattern. Because the hub is a three piece hub, it is also possible to place the hubs in any position you want, so there should never be a problem getting the holes lined up the way you want.