Where are you located? It would probably be best to work with a machine shop that specializes in Olds motors. That way you won't be getting a bunch of conflicting info from the machine shop working on your engine and people from here and/or other sites. When you are trying to get this much power out of a 350 Olds, you just need to find a good machine shop and stay with it. Do not start getting advice from a bunch of different people, or it could cost you much more money.
I also can't stress enough that you need a machine shop that knows Olds engines!! They are different than Chevys and take different techniques to make power. If you post your location, me or someone else can tell you a good place to go.
From the info you gave us, you have a good starting point. The block should be fine to use. You may or may not want to get a forged crank. To get that kind of power, any of the older Olds heads will need a lot of work, so you may be fine with them.
Just thought I would throw this out there also. If you would like to use a forged crank, I have one I plan on selling soon. Let me know if interested.