1955 Tri-Five pre-Impala Bel Air top-trim launch on the 1955-onward 115-inch B-body — 265-cubic-inch small-block at 162 hp, Power Glide Option RPO 316 introduction. Bel Air top-trim (NO Impala nameplate in 1955).

1956 Tri-Five Bel Air top-trim sequel on the same 1955-onward 115-inch B-body — 1956-only chrome-bezel egg-crate grille, 265 small-block carryover, year-specific letter-pair codes.

Bel Air top-trim (NO Impala nameplate).

1957 Tri-Five Bel Air sequel-year-2 — 283 small-block launch at 185 / 220 / 250 / 283 hp, 1957-only 283 Fuelie RPO 540 mechanical injection, 1957-only anodized two-tone paint. Bel Air top-trim (NO SS trim in 1957).

1958 Impala nameplate launch on the 1958-onward B-body full-size unibody — 348 W-head at 250 / 280 / 315 hp, the 1958-only triple-round taillight lens, triple-carburetor RPO option opens at the Impala trim.

1959 sequel-year of the Impala on the 1959-onward B-body — 1959-onward teardrop taillight stainless molding, 348 W-head carryover, and dual-quad option RPO opens on the 348 W-head.

1960 full-size X-frame carryover — 1960-only flat-roof roofline refresh, 348 W-head carryover, ROHOLM (R) trim-tag Detroit-built fab signature, DuPont lacquer / enamel paint factory chain.

1961 Impala SS trim launch on the B-body 119-inch unibody — 348 W-head at 350 hp base SS engine opens the SS option chain at the Impala trim (distinct from the 1961-only Bel Air SS 409 one-year window).

1962 SS option-chain sequel on the B-body 119-inch — 1962-onward 327 / 350 small-block SS option chain opens, the 409 W-head option continues at SS trim, ROHOLM tag continuity carry.

1963 SS sequel-year on the B-body 119-inch — 1963-only Z11 427 / 430 hp aluminum big-block homologation specialty at SS trim, 409 / 427 option chain carryover, ROHOLM-derived Oshawa-built Canada-only subset.

1964 fourth-year SS option-chain carryover on the B-body 119-inch — 327 / 350 small-block SS carryover, 409 / 427 option chain at SS trim, 1964-only horizontal blade grille and revised chrome trim refresh.

1965 SS 396 L34 / L78 stack opening at SS trim on the B-body 119-inch — L34 396 / 350 hp and L78 396 / 375 hp option chain, L89 aluminum-head optional cross-platform fitment atop the 396 block.

1966 427 big-block opening at SS trim on the B-body 119-inch — L72 427 / 425 hp option chain at SS trim (distinct from the 1965-onward 396 L34 / L78 carryover); 1966-only SS-only grille and chrome trim closure.

1967 L88 427 / 430 hp all-aluminum cross-platform fitment opening at SS trim on the B-body 119-inch — 1967-onward L88 aluminum (NOT the 1966-onward L72 427 / 425 iron), SS-only trim continuation, ROHOLM-to-Fisher Body cowl-tag transition.

1968 sixth-year SS option-chain carryover on the B-body 119-inch — 1968-onward redesigned rear-deck stamping, SS carryover at 350 / 325 hp reduced-output federalized-tier compression, ROHOLM-to-Oshawa plant chain.

1969-only ZL-1 / Z16 / COPO 9560-61-62 homologation window at SS trim on the B-body 119-inch — the 1969-only ZL-1 427 / 430 hp all-aluminum COPO homologation, 1969-only rear-deck refresh, ROHOLM-to-Baltimore plant chain.

1970 emissions-era closure of the B-body full-size SS track — 1970-only LS4 454 B-body-only fitment at SS trim (454 at 350 hp, distinct from the Chevelle LS6 / Camaro LS6 / Corvette LS6), 8.5:1 federalized compression floor.

1971 post-SS-impala continuation on the B-body 119-inch — LS5 454 / 365 hp reduced-output carry-in at SS trim, LS4 454 / 350 hp reduced-output opens, 1971-onward 8.0:1 compression floor on the 454.

1972 emissions-era closer at SS trim on the B-body 119-inch — LS4 454 / 310 hp reduced-output carryover in the SS trim, LS5 454 closure at the 1971-onward endpoint, 1972-only 8.0:1 compression-floor federalized tier.

1973 SS closure post-1972 on the B-body 119-inch — SS designation closes (Caprice shifts top-trim), 1973-only catalyst / EGR / thermostatic air cleaner / 8.5:1 compression floor lands on the 350 small-block as base.

Terminal-year of the 1958-1973 catalog scope.