Here are the flanges, they came out just right and fit perfectly, seems I got the measurements/drawing figured out. There is some slop on the bolt holes (as original) and all 4 studs center nicely in the holes. Outside contour looks good. Inside bore I had leave 1/16" small to be bored to suit later.
PICTURE

•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
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-