Putting money into the valiant, suggestions?

A roller cam can be done on a slant six, but You can build a complete engine with a regular flat tappet cam for what the roller cam alone would cost. Someware in the neighborhood of $1,000 for the cam alone. Then you would need a belt drive oil punp, and a distributorless ign, as the roller cam blanks do not have a pump/dist drive gear. Then you have the cost of roller lifters, and the rest of the valve train. Only a ultimate race engine would show any benefit from a roller cam over a good flat tappet cam. Besides the OP was talking about a daily driver, not a race car.