400 (451) in '68 valaint????

The valiant has the same engine compartment as a Dart or Barracuda which both came 383's from the factory. I've heard the shumacher kit works well but get BB torsion bars. You could get a 73+ K-frame and use the spool mounts that came on the 400. Are you going with headers or factory exhaust manifolds? If factory manifolds you will have to find the drivers side one for an A body (expect it to cost). TTI makes headers that are supposedly easy to install. Hope this helps