found this post in another forum and figured i'd add it to the archives here for others.
"This part directs ported vacuum from the carb to the distributor advance until the ported vacuum is closed off by the throttle closing. When it drops below a certain value, I recall measuring it at 7", it bypasses 7" of manifold vacuum at idle."
"The Non-Linear Valve has been renamed to Vacuum Regulator and is available at Napa for $34.49 under Part Number CRB 229722."
That's not coming up as a good number. 229720 and 229721 are