Duster differences 70-71

Yep, you got the hood pin revisions in the core support and that may have been for only hood pin cars in '71...

For 340 cars and maybe all models and options

AVS?? in 70 to Thermoquad carb and spread bore manifold.
'70s had dual point distributors, electronic in later '71
Horned air cleaner to just openings in airfilter can
340s were balanced and more internal clearance was added.
'71s had HD rear springs...6 on left, 6.5?? on right
shoulder safety belts added in '71
darker rallye rim centers in '71
same jacks, but '71 had indentions in the bumpers for the jack hook
some '71s had indentions where the radio antenna was attached.
Calif. '71s had some emission adders
gas vent tube in trunk....I think '70 didn't have a vented gas cap.
electric window washers...option or a foot pump on both years.
chrome wheel well and sill trim...option
I've heard the X and J head issue for years, but I'm still out on that. I ordered a '71, received it 6-12-1971 and it had Xs, so compression was still 10.25-10.5. Very late '71 did not have HP exhaust manifolds...they were 72 style...compression change???

There were varations in cars actually built in 1971, not '71 models built in '70. UAW striked Plymouth (Mopar) in Feb. 71. Cars were assy. to various configurations and shipped to other plants for completation.

What else?
Greg