No such thing as a true HO in '73. The 455 in 1973 was like all of the others that year. 250 HP.
Production numbers:
519 455 F37 Sport Coupes
25 455 D37 coupe
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1976 LeMans B09 Freeway Enforcer, 455/M40 Smokey
1977 Trans Am, 400/M21 Black/Gold Bandit. 44K actual miles
2017 Sierra SLT 1500 Z71 4X4 
2019 Canyon SLT Crew 4X4 
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