You could probably get a nice set of shorty's and catted mid pipe for around $250. If that's too big of a stretch for you, maybe you should rethink the mod game. It get's spendy.....and if a couple hundred bucks is gonna sting that much right now, what are you going to do when you run into real problems?
No offence, but in my opinion, if you don't have at least a $500-$1,000 cushion set aside for a rainy day/moments notice type of purchase with one of these old hot rods, you probably shouldn't be messing with one. They've been known to bleed a person dry.
To answer your question though....yes, a 2 1/2" mid-pipe will bolt up to a set of stock headers and visa versa. I don't think you're going to be overly impressed with the results of just doing one, or the other though.