The 421 was THE Pontiac motor. It was their racing quarterhorse in the early 60's. All of their later performance engines except the Ram Air 4 were derivatives of the SD 421 program.
You could also get "regular" 421's in the big Pontiacs in the early 60's. The 389's and 421's were the big motors for the big cars. Didn't 421's become 428's in 1967 when the 389 became the 400?
Yes, you could get a "de-tuned" 421 in a regular car. The 421 SD package had a solid cam and special heads.
When the 421 became the 428, the Arma Steel crank was replaced by A Pearlitic Malleable Iron crank (PMI- no relation) and the forged rods were dicontinued completely.
