Here is some parts info for you to find what you need by measuring your old one and gives you part numbers to ask for at the parts counter of your choice.
http://www2.dana.com/pdf/K350-1-DSSP.pdf
With the right catalogs likely you can do the job that any good parts guy can do for you.
I'd be looking for a better parts place if the ones you usually use can't even find a u-joint for you.

I prefer Spicer U-joints, but don't think NAPA sells them here, so ask who does in your area.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-