I was referencing page 33 out of the assembly manual. I have since found that there seems to be a misprint in the 1964.5-1965 Ford Mustang Assembly Manual on page 33, Installation-Exhaust System. Where the "Y" pipe connects to the mid-section pipe, there is a reference to the clamp that states: 5252 ASSY. 3 REQD. Well with only 3 pipe joints, I assumed that all joints were clamped.
After 2 MCA shows, I kept being told that "some" of the joints were welded. More research and a closer look reveal, although the other two (2) clamped joints (Y pipe and Muffler "in" port) are shown and described, there is no detail view of the tailpipe joint at the muffler (out port) on that page. So, I can deduce that there is a misprint, the tailpipe is the joint that gets welded and thus, only 2 each 5252 clamp assemblies are required.