Hey Fred
On my stock seat frame I cut out two small pieces of metal right @ the base of the lower back of the seat, about 1-1/8''x 2-1/2''(about the size of a seat belt buckle. These were equally spaced for three belts to fit along that back rail. this allows me to direct the middle belt(s) & buckle directly thru those two slot holes and to the 'crack' between the bottom and top seat cushions as possible. When I first installed the three belts (one for the middle passenger), the middle belts had to get routed over the steel frame (about 8'' high), then down and through the 'crack' of the top and bottom of the cushions. this did not work very well as when the seat gets re-positioned forward or back there was slack or tension in the lap belt that had to be taken up in order for the seat belt to fit properely.
I attached the belts to two new holes equally spaced along that back seat rail just in front of the gas tank using the big washers. the other two attachments were to the frame bolts that come up thru the cab (two 3/8'' along that back rail), nyloc'd.
I have now removed all the belts and bought two new shoulder belts from julanios (because their belts are a couple inches longer in length than jcwhitless'. i now see that dave also used julanios. I did because I read catologs and found their's allowed a little more 'girth room'.
http://www.julianos.com/3_point_belt_bench.html I pretty much did what dave did
also
if you buy from julanios
you don't have to buy the steel mounting kit. so that could save you some $$$ and most of us can make our own and their kit for the most part does not fit our trucks.... so wasted $$$ there.
http://www.speedprint.com/Deves50/seatbeltassembly.php the new belts use that same cutout in the seat frame but the take-up reel fit neatly down in the cabs lower 'pocket storage below the door' area. it's real hard to take a picture down there cause you can't see much, but I think I did a nicer way than dave did. he welded some attachment to the frame where as I did not... yet. I had to make a steel backing for the upper shoulder belt attachment and positioned that just above the corner window.