Dave,
I don't recall the part number. I ask for '48 Ford passenger car. I paid $52 outright about three months ago - that's the most recent I've purchased.
I do not buy their wheel cylinders. No reason other than I don't know the quality and don't want to take chance. I do know the wheel cylinders Mike Driskell sells are of good quality and his price is fair.
If you can't find the NAPA master cylinder number, let me know and I'll dig it out.