There are right and left pistons because of the connecting rod pin offset designed into the pistons.
The early MELS (58/59 and 60 in BIRD) had Hi-Compression. In 1960, the CR was cut down as they tried to make the 430 somewhat fuel conservative (2V). One would need the complete set of shop manuals and Master Parts Catalogs to discover how piston dome height changed over the years. But one thing about the engine design is imperative and that is the wedge on the piston itself. If you read theory in the shop manual as to why the combustion chamber is designed in such a fashion, you will find that the wedge as it moves upwards to the flat head surface causes the fuel mixture to be forced as a gas to be sprayed (for lack of a better term) over the ignition of the spark plug. If one uses a flat top, this feature will be negated and I would imagine a lot of HP lost. The wedge is not a pop-up feature but a necessary part of the plank head combustion chamber design.
It seems service replacements now come as flat tops, as they are easy to produce and will fit other types of engines also. If one wanted to lower CR in a MEL, it would be best to retain the wedge and put a dish in the rest of the piston stop. This will require a custom piston, or possible a copy of an early 430 piston dome. As these engines become less and less popular, correct service parts will be more difficult to come by. The same with camshafts. No one has produced blanks for years, so it is difficult to use more modern grinds.
