Pre-Impala Top-Trim Callout — 1955-only Tri-Five launch-year chrome delete Bel Air SS-precursor framing on the 115-inch Tri-Five B-body; the 1955-only 3845982 launch 265 small-block opens the 265 family.

Tri-Five carryover year — chrome-bezeled egg-crate grille (the second-of-three Tri-Five grille patterns) on the 115-inch Tri-Five B-body; 1956-only Duntov-spec SR-cam solid-lifter 265 / 225 hp high-performance option.

Tri-Five terminal year — chrome full-width egg-crate grille pattern + the historic 1957-only 283 / 283 hp Fuelie RPO 540 (the FIRST production fuel-injected V8 in a Chevrolet) on the 115-inch Tri-Five B-body.

1958-only launch-year three-round taillight lens on the 116-inch full-size B-body, opening the Impala nameplate with the 283 small-block + 348 big-block drivetrain option chain.

1959-only year-correct batwing rear-deck chrome sweep on the 116-inch full-size B-body (distinct from the 1958-only three-round taillight lens); the 283 small-block and 348 big-block drivetrain options continue the 1958-onward engine family.

1960-onward X-body launch — the X-body unibody opens on the full-size platform with the 283 small-block + 348 big-block carryover; cowl tag transitions to the 1960-onward X-body layout with 1960-year-specific letter-pair codes.

Full Impala line @ 1961 — covers the 1961-onward B-body 119-inch unibody transitions (the SS trim is the cross-cut in the guide row above; this deck covers the standard Impala / Bel Air / Caprice / Biscayne trim ladder).

Full Impala line @ 1962 — covers the 1962-onward 327 / 409 chain as the cross-cut suite outside the SS trim fitment. The 1962 Z11 427 / 430 hp aluminum-head homologation pre-cursor routes to the SS deck above.

Full Impala line @ 1963 — the 327 / 409 chain carryover outside the SS trim fitment. The 1963-only mid-year Z11 production run routes to the SS deck above.

Full Impala line @ 1964 — the closing-year 409 routes to the SS deck above; this deck covers the standard 327 chain + 1964-onward assembly-plant and bodywork carry-over.

Full Impala line @ 1965 — the SS 396 launch year routes to the SS deck above; this deck covers the 1965-onward L35 325 hp base 396 chain outside the SS-only fitment.

Full Impala line @ 1966 — the SS 427 L72 + ZL2 cowl-induction launch year routes to the SS deck above; this deck covers the 1966-onward L34 / L78 396 chain outside the ZL2 cowl-induction fitment.

Full Impala line @ 1967 — the SS 427 L88 all-aluminum launch year + the Fisher Body cowl-tag standardization first-year routes to the SS deck above.

Full Impala line @ 1968 — 1968-onward redesigned rear-deck stamping + 1967-onward L88 / L89 carryover year routes to the SS deck above; this deck covers the standard deck gate outside the SS-only fitment.

Full Impala line @ 1969 — the 1969-only ZL-1 / Z16 / COPO 9560 + SS-closure-post-1969 framework routes to the SS deck above; this deck covers the standard deck gate outside the homologation chain.

1970-only LS4 454 B-body-only fitment (distinct from the Chevelle LS6 / Camaro LS6 / Corvette LS6 line-codes) + the 1970-onward 8.5:1 compression-floor federalized emissions-era tier on the 454.

1971-onward LS5 454 / 365 hp carry-in at the 8.0:1 compression-floor + 1971-only LS4 454 / 350 hp reduced-output SS trim engine (the LS5 launch dropped from the 1970 LS5 / 360 hp high-output to the federalized emissions-era 365 hp variant).

1972-only LS4 454 / 310 hp reduced-output final-year-of-the-LS4 chain closure (the LS5 454 / 365 hp closure leaves the LS4 carryover as the only 454 option on the 1972 B-body).

1973-only terminal-year of the Chevrolet Impala on the B-body — SS trim closes post-1972 + 1973-only federalized emissions-era packaging (catalyst / EGR / thermostatic air cleaner / 8.5:1 compression-floor) lands on the 350 small-block base at L65 / 145 hp.