According to this: https://www.campyonly.com/history/1974/chainlines.pdf
There is a 1mm difference between a 68-SS-120 BB chainline, and a 68-P-120 BB chainline.
I have the 68-SS-120 bottom bracket. So the question now is, where would a campy pista chainring line up on the spindle, closer to the inner or outer chainring, or "centered" at 43.5mm?

The 68-SS-120 is a road spindle, intended for use with double chainrings. If you're using a road crank, running the chainring on the inner plateau should give you a good chainline. If you're using a track crank, you'll want the 68-P-120 spindle (unless you have an old frame with 110mm rear dropout spacing, in which case you'll want the 68-P-110).

I want to use a track crank on a road spindle. The link above indicated that the 2 chainlines are only ~1mm different, assuming my track chainring is at the 43.5 road chainline. I don't want to spend big $ for a track bottom bracket just to perfect my chainline by a millimeter.

If you already have the parts you're proposing to use, you have nothing to lose by trying it.

I did - I think it's pretty close. I measured a hair over 43mm at the chainring, and right at 43mm at the rear cog. I put a 0.5mm spacer between the cog and hub. I haven't ridden it yet but hopefully it will run smooth and silent. Also, there was only ~2mm clearance between the chainring and chainstay. Here's a pic, taken just a few minutes after I finished.

Very nice ride.But i wouldnt worry at all about a 1 or 2mm diff.