67 383 Dart

Imho. If a 383 (any variant) can't spin a dart''s tires than the heads are the least of the problem.

Areas to look at:
Rear gear ratio
Tall tires
Trans slipping
Carb issue
Ignition timing
Engine timing
Flat cam
Lifters bleeding too quickly

Probably 50 more issues that it could be

Again just my opinion...