perportion valves, master cylinders, etc.. all do the same freakin thing.
Only mystery is plumbing correctly.
As for buying calipers locally to save shipping, you'll pay more in core charge if you dont have 2 for exchange.
The whole prop thing has always had me befuddled. My car was originally a drum car all around and it has the valve that disk cars are "supposed" to have. Every thread and internet search I have ever done has told me I have the wrong one! I'm using it and havent had any problems after switching to disks up front. Now I have two because I never used the one I bought to replace the one I already had.?!