400's are they any good?

Mag-mind;

To a degree, your right. A tight quench is good, but not needed. It's just the later and other low compresion engines lack the ratio to run a bigger cam. Most cams are not ground for use on low compresion engines and this is where the mistake comes in.

The cam selection is not fully thought out. The timing events must be thought out before the purchase is made and the cam slid in. Just grabing a Purple 284 and expecting added performance can be a bad move. That cam is a poor choice on a low ratio mill.

Places like Hugesengines advertise on there site a cam for such a low ratio mill. The timing events are customized to add cylinder pressure. Then, like James was saying, milling the heads down some will add help to the mix.

The stock engines should allready have the thin gasket, but, the replacement gasket in kits or blindly ordered will be double the thickness. Having the gasket first so you know you have it will help speed the work. Sometimes, there not easy to get. IDK why, but I have seen complaints here time to time on it's availability.

(The SD Ponco T/A's focused on mad torque production in that 455. And the Poncho motors sure made alot of that! My fav is the 5spd car, Blue and White)