You can use the same mounting locations I used with plain strap belts.

If you think about how a seat belt should work you don't want it passing in and back around and under stuff, they should be pretty much straight line to your lap.
The locations I chose allow that as best you can do in an AD truck, in my opinion.
I felt that mounting the center ones to the cab floor right close to the seat riser, large washer underneath, was stronger than bolting to the seat riser alone. (also don't have to remove gas tank to bolt them in)

Whatever you do Install them as safely as possible to suit yourself.

•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-