Are all 1972 Pontiac 455 engines considered HO?

No, not all 1972 Pontiac 455 engines are considered High Output (HO). The 455 engine was offered in both standard and HO configurations during that year. The HO version featured higher compression, a more aggressive camshaft, and enhanced performance characteristics, while the standard 455 had lower output and different tuning specifications. Thus, only the specific 455 engines designated as HO are classified as such.