Are the 77 and 78 dash gauges interchangeable?

Totally. Functionally in every way. Same mounting. Connectors are the same too. There was a font change on the gauge faces, but I think that happened sometime in 76-77 transistion.

Cool! Thanks

I thought the 78 Speedo has a thing on the back that affects the emmissions? I think it connects to the BCDD?

I will check with my Z mechanic buddy today and post what I find. Thanks TomoHawk. How is your EFI system performing? Mine suck's right now!

If there is additional components on the speedo, would be simple to transfer the sensor package on the back to the new one.

My thoughts also zKars.

My EFI is working just fine. The engine isn't so happy when I try to start it in 30-degree air tho.

Do you have strick smog laws out there in Ohio? We do here in CA. 0.5% CO at idle and part throttle. That is really lean for my Z. And it is stock.

Yes, there are smog laws, but no smog ether. Ohio has beautifully clean air, unless you live downwind to a cow-barn or pig-barn.