Holy cow Fat_Mike.. that link is a 'deep dive' into the D/Dart program.. and thanks Jim and 6pak for the info.. that's probably why online decoders are unclear.

.. there are a lot of unexpected details for 1966 codes..
I wonder if it's any clearer for Plymouth A-bodies - because they came up with the Barracuda's Formula S package in '65. Plymouth probably coded that package clearer. IIRC the Plymouth Barracuda Formula S package is an F7 on the fendertag.

So yeah, mr_340 ... Dodge did it differently and came out with the rare 1966 LO23 Super Stock D/Darts which I'm guessing would have the 'S' code on the 275hp 273 block ..

In 1966 a Dart GT could be ordered with the exact same features as the Barracuda Formula S, and that's what we are thinking my brother's Dart GT has, not that the VIN or fendertag is going to list it the same as a Plymouth. His Dart has disc brakes, sway bar, probably the 273HP engine, and dual exhaust. My brother says none of it looks aftermarket - though I'm not sure his dual-circuit brake MC is original for 1966.. anyone?
I *think* his VIN is an LH23, but I'm waiting for him to let me know for sure.

Online Decoders are not consistent - I see decoders saying a Dart GT is LP23, and LH23 for the Dart 270, and LL23 for a 'plain' Dart.. but others say there Dart GT is LH ..

It seems his best evidence for now is going to be the engine number code stamped on the block under the driver's side head... if he can read it clearly.

I'll start decoding his Fendertag.
- Art

Here is another cool picture.. He applied for a vintage plate from the country he lives in, and check out the awesome number he got!