What carb to buy?

Unless you're going to change the cam, port the head, and run headers, I'd leave it alone and keep it a 1bbl. for the street. The 2bbl eats more gas and only gives a tiny performance gain on a stock motor. Too convert to a stock 2bbl setup you'll need an air cleaner and 2bbl. kickdown linkage too.....

I gotta disagree with you on the 2bbl eating gas. A lot of people get better mpg's with 2bbl's, especially around town. You really gotta stomp on a 1bbl to get it up to speed from a stop, where you just have to roll into a 2bbl. It's not a huge performance gainer but you can definitely tell the difference. You don't need headers, just a 2 1/4" exhaust to get the full performance out of it.