Complex sentence: The first generation Pontiac Sunbird was a rear-wheel drive subcompact, H-body varient of the Chevrolet Monza, based on the Chevrolet Vega and shares Vega's wheelbase and width.
Split into simpler sentences: The first generation Pontiac Sunbird was a rear-wheel drive subcompact car, H-body varient of the Chevrolet Monza. The H-body Sunbird is based on the Chevrolet Vega and shares Vega's wheelbase and width.