What should I do?

I've posted a couple of questions on FABO before and have always gotten great advice. I have a 67 Barracuda S with the original 273 Commando in it. I recently upgraded the intake (eddy performer) and carb (Holley 570 street avenger) because the previous owner destroyed the originals...

Now comes the time to start doing real work on it. The engine is in serious need of a rebuild (lots and lots of sludge and serious lack of performance), so I plan on beefing it up a little in the process. I am not a car tech guy, but love my car and want to learn so be gentle...

From what I have found out, I have a 8.75 rear end and a 904 trans. I would like to get 300+ out of the rebuild, which, I believe, is do-able.

Anyone have some combo suggestions? I have a feeling that a rebuild will actually cost more than a swap, but I want to keep what's left of the original equipment in it if possible.