The new intermediate-based 1969 Grand Prix began to take shape in April 1967, with a few prototype models built on the full-sized Pontiac platform before the G-Body was ready.
To save both development costs and time in much the same manner Ford created the original 1964 Mustang using the basic chassis and drivetrain from the compact Falcon, the revised Grand Prix would have a unique bodyshell but share the A-body intermediate platform and mechanicals with the Tempest, Le Mans and GTO.
This reduced development time from the usual 36 months required for a new model to less than 18 , allowing Pontiac to concentrate upgrading styling and interior appointments.

Shortened by three inches from the previous Catalina wheelbase, the 118 in (3,000 mm) 1969 Grand Prix finally had its own body – and Pontiac's longest-ever hood.
Like all but the short-lived 1967 convertible, the new Grand Prix was a 2-door hardtop.
Model names borrowed suggestive Duesenberg Model J nomenclature for "J" and "SJ" levels of trim.

The basic 1969 body shell saw a major facelift in 1971 bracketed by minor detail revisions in the 1970 and 1972 model years.
The new intermediate-based 1969 Grand Prix began to take shape in April 1967, with a few prototype models built on the full-sized Pontiac platform before the G-Body was ready. To save both development costs and time in much the same manner Ford created the original 1964 Mustang using the basic chassis and drivetrain from the compact Falcon, the revised Grand Prix would have a unique bodyshell but share the A-body intermediate platform and mechanicals with the Tempest, Le Mans and GTO. This reduced development time from the usual 36 months required for a new model to less than 18 , allowing Pontiac to concentrate upgrading styling and interior appointments.
Shortened by three inches from the previous Catalina wheelbase, the 118 in (3,000 mm) 1969 Grand Prix finally had its own body – and Pontiac's longest-ever hood. Like all but the short-lived 1967 convertible, the new Grand Prix was a 2-door hardtop. Model names borrowed suggestive Duesenberg Model J nomenclature for "J" and "SJ" levels of trim.
The basic 1969 body shell saw a major facelift in 1971 bracketed by minor detail revisions in the 1970 and 1972 model years.
Pontiac Grand Prix