This is from '73 Dodge Chassis Manual and will give you a good idea of what to look for.
18" diameter, 7 blades, 2" wide. Also used on 225, 318, and 340 E, B and C-bodies.
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This is from the '73 Dodge Parts Book.
It does not show the 5 blade flex fan on a 318 A-body, but that's what you have on there currently.*
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V, L = Valiant, Dart
BJ = E-body Barracuda, Challenger
R,W = Satellite, Charger & Coronet
P,D= Plymouth, Dodge (full size)
* Just to satisfy curiousity. here's the models/options that the '73 Dodge FSM shows using that flex fan
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