my 70 has the snap in shoulder strap. It doesnt seem to work that well because it doesnt stay snapped in. But that could very well be because my car is nearly 40 years old. As for my 69 I dont have the shoulder strap but that ver well could be the PO's doing. I would have to look at my lap belts to see if they have the hole that the shoulder strap connects into

 

The seat belt option does not show up on my marti report, but maybe it would not. The PO put in a cheap set of retractable 3 point harnesses, but they are junk. I am not sure if I would trust my life to them in a serious situation. I will do some research and try to find some era correct belts that mount with a shoulder harness.