One advantage to a ready made one piece fitting is no chance that a restriction plug can work loose inside of there isn't one.
Another advantage is for someone following instructions it may be difficult for them to drill and tap things, and so much easier to order the ready made part.

Just providing other options.

•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-