This is aimed at Chas., or anyone else who wants to jump in.

My Capo Sieger has its original Campag. Gran Sport derailleur, and I have nice aluminum Simplex 49, 47, 46, and 45 (minimum size for the 3-to-6-bolt mounting adapters) tooth chainrings for the original Agrati cottered crankset. I have attached a photo to give an idea of the derailleur mounting tab length and rear derailleur orientation.

Option 1 (guaranteed to work): 49-45 / 14-17-20-24-26.

Option 2 (low gear - jockey pulley cram job): 49-45 / 14-17-20-24-28.

Option 3 (12-speed, using an ultra-6 freewheel): 49-46 / 14-16-18-21-24-26.

Option 4 (12-speed, lower bottom end, also ultra-6): 49-46 / 14-16-18-21-24-28.

Question 1: Will I be able to set the wheel position and chain length to make Option 2 work? This gives me about the same bottom gear as the 42/26 I run on the Bianchi and the Peugeot.

Question 2: Will the (option 3) ultra 6-speed work w/ this derailleur? I tried a test fit, and it looks like I need about 2mm of drive side spacing on the rear axle.

Question 3: How about going for the home run, with option 4? Now I am looking at both the 6 speeds and the 28T low gear cog.