Seatbelts in 47-54 trucks

[DieselRat]

Getting to the point of finishing up my interior and I need to add seatbelts. Would like to do a 3 point, using the original bench seat and frame for now. Ive seen some of the aftermarket kits but I just wanted someone with some experience to say what to look out for etc.

I could see how bolting them to the floor is simple enough with some added bracing, what I'm not seeing is how they would attatch to the sheet metal up at the shoulder area. My truck is a 54 GMC thats never had any seat belts added. Thanks for any input.