What carb to buy?

I would try and find a NOS Carter BBD. There's plenty of parts and info on them, they get good mileage for a daily driver and most people are familiar with them and will be able to help you out if problems arise.

If you go looking for one, remember you have to get a slant six BBD. The 318 BBD's are basically the same except you'll have to fabricate a linkage to pull the choke off. Also some of them have holes in the throttle plates that you'll have to close up.