Base Camaro is the volume car under the Z28 and IROC-Z performance trims. Same F-body unibody (FP-prefix VIN, F87 coupe body code, F67 convertible from 1987 on), same MacPherson-strut front + torque-arm-with-coil-spring solid rear axle, same brake hardware family; what differed was wheel-tire spec, sway-bar diameter, optional disc-rear-brake spec, and the engine + transmission combinations available.
Engines spanned the LQ9 2.5L Iron Duke 4-cylinder (1982–86) at the bottom, the LC1 / LB8 / LB4 V6s through the run, and the LG4 carbureted 305 + L03 TBI 305 V8s as the affordable V8 path. The hot V8s — LB9 5.0 TPI, L98 5.7 TPI, L69 5.0 H.O. — required the Z28 trim for most of the run.
Plenum decodes a base Camaro from the SPID the same way it decodes a Z28 — the SPID label is the same template. The Z28 / IROC-Z / 1LE distinguishing markers are package RPOs (Z28, B4Z, 1LE) that appear or don't on the SPID's option block. A VIN that lacks any of those package codes resolves to base Camaro Sport Coupe.