Ok, taking them one at a time:

1) Belts coming off. You need to put something like a carpenters metal square across the grooves in the pulleys to see if you can determine what is off, if anything. Most likely culprit is the alternator or some accessory like power steering belt or ac belt (if so equiipped). The water pump pulley and crank pulley are pretty much fixed and so long as they are original that alignment should be ok. But with a 42 year old car anything is possible and you have no way of knowing what may have been changed during that time.

2) Carb on that was a Rochester Q Jet, I think. What does it have on it now? Are you looking for an absolutely correct carb or just one that will run properly?

3) What is this "tail fin" you are referring to? Didn't know 69 Olds had fins.

4) Someone like Coker tire will be your best source for tires that are what were on the car when it was new.

5) Hole in exhaust........you're on your own on that one.

Don