[JoeC]

Phase III was a general term used on many items including complete cars, hoods, ign boxes, and many other Motion items. The Motion engine packages were more specific.
In the Motion Phase III Racing Engine catalog the Phase III ZLX 454 575 hp engine spec sheet list shows ìspecial Cast Iron open chamber cyl heads with a note ìour most popular engine packageî. They also list a Phase III ZLX 454 625 hp ìfull competitionî engine ìsame as aboveî but with 2x4 tunnel ram and .600 plus lift cam.
Another note lists the alu heads as $300.00 option available on all BB engines.
There is another ad for ZLX heads decribing them as cast iron open chamber heads same design as sec design ZL1 alum heads. From what I can tell in the Motion info, the basic ZLX was all cast iron then you would add the alu heads as an option as you could have done with other engines. I am sure Joel did not worry about exact names such as Chevy did where the alu head engine would get its own name such as RPO L89.