[StingRay]

Consider that in 69 when GM put true buckets in that they reinforced the floor. A non bucket truck does not have sufficient floor strength for a set of bucket type seats without a similar degree of reinforcement and that is to get to 1969 standards. I'd start there for anything bucket related. Pics of the factory reinforcement have been posted over the years and I've occasionally seen the parts for sale on the classified board here. For other than stock bench type retrofits just doing like the factory did will for the most part be fine. Our trucks are outfitted for 3 point belts from the factory and there are many options available for using these factory installed fastening points with modern retractable belts.

When it comes to integrated belt seats I honestly wouldn't do it myself. I try very hard to avoid it in my own designs for RV's as the combined loads for the pull tests are huge. Consider that on one of the last single seating position (rear of vehicle) belt only tests in pure tension we lifted the van off of the ground. I'm talking a completed chassis not some stripped down body in white with no drive train or interior. Most of the force was actually directed forward not upwards. You create an enormous amount of leverage by using the seat for the belt mounting point which makes it far worse. You also have to contend with both tension and compression forces where as with traditional belts everything is tension and just anchor points. Reinforcing for integrated belt seats requires significant reinforcement and spreading of loads. If I was to start somewhere I'd start with at least 1 1/2" square tubing and make sure I was connecting to structures like cab/floor supports and rockers making sure I had added plates on those structures suitable for attaching to. Most of the tin under our trucks by itself is not of suitable thickness to attach to by itself. You are really talking roll cage level of construction but below the floor.

The trucks these integrated belt seats come from have the advantage that the floor stampings have the shapes needed for appropriate stiffness built in where it needs to be and the material is high strength steel. Our trucks floors are pretty flat. It takes a lot of tubular material, heavy plate and creativity to make up for a cad/fea engineered stamped shape.

The other thing that must be considered is what shape are your floor, rockers, cab corners and cab supports in. Even stock seats and belts need 100% rust free structure to be truly safe. If considering non stock or worse integrated then don't even think about it until your cab is completely sorted out.

Witness a floor fold up like origami some time and it puts a whole different perspective on safety for you. Thankfully I've never had to see one of my own designs do this. I've never failed a destructive test in 18 years.

A significant change in your spacial relationship to other parts of the cab is a very dangerous thing. Worse is to lose it altogether be be ejected from it either by yourself or still belted to the seat.