Clogged up ports???

It's an exhaust crossover and it gets clogged by carbon deposits from a rich mixtuire and burned oil getting by the rings and valve seals. On a street car or if you're going to run the stock type choke, I'd open those passages up. While you have the intake off, I'd take a good look at the cam. If it's sketchy at all, I'd replace it and the lifters. Seeing as how you're putting a 4bbl on, it might be a good idea to get a more aggresive one anyway.