runnjump,
Welcome to the site. Although I don't know the answer to your question, I will say that a 100 RPM difference is quite insignificant.
The availability of the proper unit could be a sticky wicket...because this item responds to engine vacuum, the difference must be achieved with the internal spring.
Unless you are attempting to do a matching numbers thing, I don't think you would ever notice the difference between these two vacuum advance units.
Stuart
