Seatbelt attachment point question

[fryer1979]

As I plan to use my truck for more than just an occasional around town, I am wanting to add more than a basic lap belt for safety. My thought was something like what would have came stock on a late '80s or early '90s GM pickup, or a basic 3 point lap/shoulder belt. Mounting the floor points are easy enough, but my question is what would be recommended to mount the point that usually goes over the shoulder? I haven't been able to get an answer by searching, so any info would be welcome. Thanks