Upgrades to my stock 273 67 Dart GT

Makes more sense, but doesn't the OP' 67 273 already have closed chamber heads, and 273 are pretty decent flowing heads especially on 273 cid.
Yep, these heads with 1.94/1.88 in and 1.6 exh valves along with bowl blending and a gasket match will increase performance along with a recurved mopar performance electronic ignition setup. It’s performance that doesn’t wear out.

After that I would look into the 4 barrel setup and a quality header exhaust system.