318 won't rev past 3000 rpm

Just this past April my Dad decided he wasn't doing anything with his 67 Dart GT 2 door, so he gave it to me. It's sat in his garage for the past 14 years, getting started every 6 months or so. What's amazing is that it only needed the license plate light to pass the Ontario safety.

Cruise nights have been fun, but soon realized it was running into a brick wall at around 3000 rpm. Car would pull awesome to it, but act like it was hitting a rev limiter.

Just looking to get pointed in the right direction on this, and where I might start troubleshooting.

Known items:
Will do this in park or driving down the road, doesn't matter.
Electronic ignition, chrome box if I remember correctly.
Holly 600 cfm carb /w vacuum secondaries.
Full length headers, dual exhaust.
LA 727 auto.
Tuned to 14 deg. at 700 rpm idle. Good vacuum showing on gauge with no fluctuations.

Unknown items:
Cam specs
Head castings (guess it wouldn't be hard to pull a valve cover to check this).

Thoughts, gentlemen?