Old Campy Freewheel and Derailleur

[sailorkevin]

I own a 40-year old CIOCC 'Designer 84' that I ride occasionally just for grins. I want to replace the original 6 speed freewheel (13-20) with something a bit bigger such as 13-26 or 13-28. Three questions for you classic bike lovers:

1. Will the original Campy rear derailleur (see pics) accommodate the wider range? There are no serial numbers or identifiers on the derailleur that might help me look this up, so it seems I have to simply eyeball the length of the cage.

2. Could I go up to a 7 speed freewheel? The rear spacing of the dropouts and the downtube shifters will be ok. I wonder if the derailleur could handle the wider range.

3. Lastly, do you know of Campy-compatible manufacturers? Original Campy stuff from this era is insanely expensive. Specifically, I'm looking at this Interloc.

https://www.modernbike.com/product-2...iABEgLJEfD_BwE

Many thanks,
Kevin