There is no advantage to grooving the lifter bores at all that I know of. In fact, what you want to do is sleeve the lifter bores in order to restrict the amount of oil going into the valvetrain.
Lack of oiling has nothing to do with valve failure on the Cleveland. It is just an inferior valve design that the hydraulic cammed 351c's have.
Put a set of closed chamber iron heads on the car (as George recommended). That alone with perk the car up substantially.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.