Any chance that it's pnp?
It can be done, but it's not PnP. The plug will physically fit, but the pinout is different. That's a 4-cyl tach too, there might be info somewhere on converting it to a V8 tach.
This. I did it in my '83. Check the pinouts of the connector, and configure accordingly. There is also no provision for the auto shifter indicator on the turbo tach (all were floor shift).
I was swapping out the 5.0 for a 2.3T, so the tach wasn't an issue. I did look into it when I swapped a TC cluster into my '80 XR-7 that had the 302. Never dug into it enough to get it configured properly for the 8 cyl.