Frogbutter 

To quote Velo Orange
"Generally, it is the crank model, not the frame, that determines spindle length; so check what spindle length the crank manufacturer recommends or measure your old BB. If between sizes, it's usually wise to choose the longer."

I have a nice Campy NR crankset but not the matching BB. I have removed the cottered BB and plan to install a square taper BB for the crankset.

Question: What spindle length did Campy recommend?

repechage

To determine, one needs to know the date code of the drive side crank arm.
On the back side, there will be say, strada followed by the crank length alone, or a number in a diamond, or a number in a circle, and lastly in a square.

Frogbutter 

I was told it was a matched group. Date code on the rd is 1973. I can check the crank when I get home. Sitting at the gf's place and was bored and this question has been bouncing around in my head.

Ex Pres 

If it's '73, then 111.5mm. But just in case something's been changed, is your front derailleur lipless (old), or with lip (post CPSC '78)? If you have a lip, it's better to go with the longer one (114)