Yup, everyone has posted good stuff. Also - the 383 2bbl engines had an advertised compression ratio of 9:1 while the HP engines had a 10:1 compressiom ratio. The 2bbl pistons had a "dish" design while the HP pistons were flat tops. The 10:1 engine in 1969 also had a positive deck height which means the top of the piston actually protruded above the block deck when the piston was at TDC. The 2bbl engines had a negative deck height which means the piston top was down in the bore, below the deck, at TDC.
The engine in my car was originally a non-HP engine that has been beefed up with high compression pistons, bigger cam with matching valve springs, 452 (later model) ported heads with oversized valves, better intake, carb and exhaust. In 1969 all the big block engines used forged steel cranks. Chrysler was smart in that all the parts per engine family were interchangeable. No special heads or anything like that. The 440-6bbl used the same heads as the 383 2bbl. The difference was in the valve springs. The 383 2bbl, 4 bbl non-HP and 440 non-HP did not normally have windage trays in the oil pan and all used the same cam, too. It was milder than the RR cam in both duration and lift. The 440-6bbl cam used the same cam duration and lift specs as the RR cam but used special tapered lobes and lifters which helped reduce cam wear due to the need for stiffer valve springs in order to get 500 more rpm than the standard RR cam. Like droptop said - lots of little things went into the design of the HP engines. Chrysler engineers really knew their stuff when it came to what made these engines work.
