340 forged steel crank.

The 318 forged crank I have now he says will need 2 sticks of Mallory. I have a HD 318 cast crank from a 72 truck that has the crank pins already drilled. He says it will need Mallory also cause the 318 has a lot lighter piston. It did also have the HD rods. I can’t see putting Mallory into a cast crank. But that may be my best option. Kim