I did a search, and I could have sworn I read a Tec-Tip on seat belt install, but now I am unable to find it. I too am at the stage of seat belts for the 1941-46 truck. My preferences are aircraft type, “Lap Style”. http://www.sjtsa.org/TYPES%20OF%20SEAT%20BELTS.pdf
I have thought about chassis/floor reinforcements, but sure would like anybody’s photos or thoughts on how they did it.