1968-onward Buick 400 cu in NAILHEAD-derived cast-iron V8 (1967-1969 displacement, distinct from the 1965-onward 401 NAILHEAD that closed with the 1966 model year, and distinct from the 1970-onward 455 cu in torque-stroke); the 1968-only Buick 350 cu in small-block GS 350 fitment launched alongside the 400 as a 350-fitment alternative; the 1968-onward Fisher Body cowl tag body-code prefix (Skylark / GS car-line, distinct from the Chevrolet Chevelle / Pontiac LeMans / Oldsmobile 4-4-2 cowl tag body-code prefix on the same 112-inch A-body wheelbase).

1970-only Buick Skylark GSX Stage 1 homologation special — the 1970-only Stage 1 cylinder head casting / Stage 1-specific intake manifold / higher-lift camshaft / 10.5:1 compression on the 1970-only GSX body package (functional hood tach + Rallye stripes + GSX grille / trunk trim).

1970 Stage 1 produces 510 ft-lb torque / 350 hp.