1972 Blazer 3-Point Seatbelt w/ Roll Bar Options

[vespaholic]

I have a 1972 Blazer with the factory lap seat belts.
The truck has a roll bar.
I plan to never run the hardtop on it.
I'd like to put in 3-Point retractable seat belts in it using the factory lower holes and mounting the top part to the roll bar.
I'm going to a truck salvage yard on Saturday to look for something that might work.
Anyone have any suggestions?
Anyone do something similar?
If so what did you do?
I'm looking to do this on the cheap, so I'm not looking at the aftermarket companies for new belts.
Thanks in advance !!