I'm not condemning it, but the reality AND dependability/longevity of 400 HP is damned near impossible.
The 273 BY FAR is one of the most costly mopar sb to increase HP on. What did the D-Dart get 275hp? Did it even get 300?? And that was a BUTTLOAD of engineers and $$.
Here is a great read from a very knowledgable guy from back in the day.
Paul Cessarine(chk spelling on that).
Oh and our 67 cuda is an S that came factory with Commando, just so you know I ain't slamming it. Just a reality check.
273 Camshaft Specifications