Critique/suggestions on 273 engine build

First off, I know many of you will say to just get a 360, but I want to build the 273. The engine only has maybe 4000 miles on a rebuild. It was rebuilt with a mild cam by the PO and has an Offy intake and Edelbrock 600CFM carb and electronic ignition. My goal is to get 300-350 HP/TQ on a budget. Here's my ideas:
Comp Cams XS268S (.488"/.501" 230*/236* @.050) or
Comp Cams XS274S (.502"/.511" 236*/242* @.050)
KB or TRW flat top pistons
Mill heads to 52-54cc
Port heads
650CFM carb (Edelbrock?)
Headers (TTI or Spitfire)

I want to stick with the intake I have to save cost. It's in a '64 Barracuda, but the heads are from a '66 Commando, so have the later intake manifold bolt angles. Does this look like a good combo? Any Suggestions? (remember, it's a budget build) Estimates on the power this would make?