[Bayer Z-11]

First there were only 50 factory built ‘63
Impala Z-11s. Not 57.

Regarding the ‘62 aluminum front ends they were not installed at the factory. They were a service package item only Same as the intake, valley tray and heads released to a select few racers. There were no “Z-11s” in this model year.

Regarding ‘61 409. They were small port heads, solid lifter cam and aluminum intake with a single AFB. They were rated @ 360 HP when built. The 2x4 big port heads became a service package item late in the year just prior to the ‘62 model run.