Do you have the original half shafts or the Spicer replacements? Chuck Melton's website has comparison photos at:
http://www.geocities.com/pantera_project/HalfShaftCompare1.html Original U-joints are available from the Pantera Vendors.
Spicer U-joints should be available at your local parts house. SOBill Taylor's database has numbers for the Spicer parts. That is available at:
http://www.members.aol.com/sobill/ I downloaded the "Pantera_Information.xls". That is an Excel file. I think the "Pantera_Information.zip" is a Word file.
Are the yokes worn? Mine were bored oversize so I had to replace the half shafts. At the time I did mine, PI Motorsports had the best deal on half shafts. Check your vendors for current prices. Or ask me how to contact Mike Romine at Atlanta Powertrain.