‘66 Barracuda- odometer works, speedometer does not

Hey all! New here and new to A bodies, but not new to later Mopars (mainly Jeeps). Picked up a modified 1966 Barracuda with a swapped in LA 360, A-833 trans, and 8-3/4 rear end (3.91 gearing). Pics attached for viewing / criticism

As the title states though, when I bought it the speedo cable was not hooked up (and now I know why). So I hooked it up to see what I’m dealing with. The odometer functions, albeit clearly not the right tooth speedo gear with how quickly if adds up, but the actual speedometer doesn’t work.

Curious if others have come across this before and know what I’m dealing with here. Is it a new instrument cluster entirely? Or does the gauge come apart and just something in there that I can replace?

Appreciate it and I look forward to contributing (not just taking) in the future!

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