Here's the write up on installing my seat belts, with the pictures.
https://www.stovebolt.com/ubbthread...ve-improve-drive-repeat.html#Post1162006

The mounting locations I chose have significant structure around them, so use the large washer or nut plate on the bottom as supplied with the belts and should be plenty secure.
Again, may as well use shoulder belt. Same details for the bottom mounting points plus one at your preferred height in the door pillar.

•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-