1968 Chevrolet Impala Convertible. Full-size Chevrolets received their annual restyling, yet changes were minor for 1968. Length grew just one inch along with some minor additions of new models and the deletion of other less popular ones. The Impala convertible was the only convertible available in the full-size lineup, though an SS version was no longer a separate model having been relegated to an option package. Cost new, $3,197 before options.