The best Musclecar year was....

[69HemiGTX]

Umm... I don't need to explain my opinion, do I? However, 68 is my personal favorite year because of the new Mopar B body styling and the intro of the Charger R/T, Road Runner, and Super Bee. But yes, 69 was the peak IMO.

BTW, you forgot these:

1969
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1. The Charger 500 is built, leading to the development of the Cyclone Spoiler II and Torino Talledega.
2. Dodge builds M-code 440 Darts because Mr. Norm did it in 68, one-upping the factory engineers by proving it could be done.
3. Plymouth answers Dodge with the 440+6 Road Runner.
4. The Dodge Dart Swinger bursts onto the low-buck compact musclecar scene packing the 275hp 340, surprising many big blocks on the street.

1970
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1. Plymouth builds the Road Runner Superbird to compete with the Dodge Charger Daytona and bring Richard Petty back from Ford.
2. The 440 Six Pack is made available in all B and E body performance cars (except AARs and T/As).
3. Plymouth introduces their budget screamer: the Duster 340.
4. The AMC Rebel Machine debuts.

Sorry to be so Mopar lop-sided, but you nailed down the significant Brand X cars pretty good.