Early Thermactor AIR Vestiges
Up to MY1974, the Thermactor AIR system on 335-series
(351C and 400) used the ports at the rear of the cylinder
to inject fresh air.
The M-block intake manifold was redesigned in 1975 to use
ports at the front of the cylinder heads for Thermactor AIR,
but bosses for the earlier system remained at the rear of
manifold. They were adapted to serve as mounts for
throttle brackets, automatic transmission kickdown rod
and body-to-engine electrical grounding straps.