left twist drill bit?
I agree 100%1) If you have not done this before you will be way ahead to wait till you can afford a pro fix. It looks like it already has had enough amateur work. This can still be saved. But not likely by a amateur. The more you f it up the more it will cost in the end.
^^^ If you can find a lifter block from a 77 and up would make this go much easier, they don't use the taper screws...Find a machine shop with EDM (electrical discharge machining) machine.
Is the hole tapped into the cam chest or is it blind. If it's tapped all the way through, you might be able to get it out "fairly" easily.
You can drill though to the cam chest.
If I were gonna try it myself, I'd use the lifter block for a jig. Bolt it on with the three good bolts, use a piece of tubing to sleeve the bad hole in the lifter block, center the drill bit and slowly drill the center of the broken bolt out until what remains in the cases is relatively thin. Since the hole is already off center and looks to be in the threads, once you get the center drilled out you should be able to crush the remains of the bolt inward and remove it.