I think I f'd up

While everyone should have copies of the factory service manuals for their particular car, sometimes (a lot actually) the information and/or drawings you're seeking are just not going to be there.

I've just gone through mine (76 chassis and body, electrical) not found a single specific drawing or procedure detailing the cowl to dash brace or the pinch clamp studs (bolts) bolting the steering column up. Perhaps this is because the factory service manuals are for all car lines and just not the A bodies. Perhaps the information is in a specific manual devoted to actual body construction not generally available to the public, but I couldn't find a single diagram detailing the dash brace/pinch clamp bolt assembly in the service manuals for V and L car lines (A bodies).

If you've sheared off the two pinch clamp mounting studs, there is no magic bandaid fix and you are going to be replacing them. Maybe you'll get lucky and find some special clamp that would allow you to press the studs up out of the dash frame to cowl brace or maybe you'll have enough room to trim what's left of the studs and use coupling nuts and more studs to extend them. Be prepared to remove the dash frame (enough people on here have posted threads on dash frame removal doing a thread search should show you what you need to do) and possibly the pedal bracket too just to gain access and working room if the studs are crimped or welded to the brace, and if that's the case you might find it easier to remove the brace from the cowl and replace it.

Just think of the experience as a chance to learn more about your car and/or speed up the time line for doing some things you were going to do anyway.