I tried to adjust the valves and had no luck turning the adjusting nut.

Are they interference like the earlier engines or is that a locking nut to be loosened and then the pivot adjusts somewhat like the adjuster on the steering box?

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.