The 68 truck block I have has a forged crank luckily but has the light rods , I do have an 89 truck roller cam truck block with hopefully the stronger rods but wonder if they are Worth resizing and balancing up with the KB 399 pistons
How strong are you building for? If you use heavy rods your machine shop might have to add mallory metal to the crank to balance it. (expensive) Get some Performance I or H beam rods if you feel the need.
