The 1953 Packard Balboa-X, as it was officially called, was a hardtop based on the Packard Caribbean convertible. The main point of interest on the car was the canopy-style C-pillar. Caribbeans never recieved a hardtop like the Balboa's, but they got a conventional one (covered with Hypalon) in 1956.

Drivetrain of the Balboa-X was stock Caribbean with a 327 c.i. Straight Eight that was distinguished from lesser Clippers Deluxe's engine by hydraulic valve train adjustment, and from the more expensive Patrician 327 by 5 instead of 9 main bearings.

source: wikicars.org