[Irish1941]

They will 100% NOT fit.
Truck belts bolt to the floor and Blazer/Jimmy bolt to the lower B pillar.
Full size Blazer/Jimmy are there own design.
There is no cross reference seat belt for them from any other GM truck or car.

That being said, the LH and RH retractors will interchange with some internal work. That's another story though.

Anything pre '89 will bolt in with female floor ends you have. Back to '78 if I remember correctly.
After 1989/early '90 is late 90-91 only. GM switched suppliers and they are different.
You would need the 90-91 female ends as well to make it work. They have the orange release button vs GM plastic buckle.
90-91 belts also did away with the retractor plunger on the door jamb. It was biggest problem with those belts. Get full of dirt and stop retracting.