I have a 70-71 8K tach with redline at 6500.

I also have a 72-74 7K tach with redline at 5500.

#s on the back of each match yours.

clearly it's not a vendor/supplier issue because all the different tachs have the same vendor #.

The fact that these different tachs share the same part # tells me that the factory was only keeping track of one kind of tach. meaning that they probably did not care to differentiate between BB/SB or auto/manual trans or performance/plain jane, one part # = one tach and a car either got one or it didn't. If you ordered one over the counter you could end up with any one of them. It would seem then that each tach superceded the previous one. The 5500 redline 8K tach probably came between the other two making it late 71/early 72.

It wouldn't have come from a 74 360 four barrel car would it?

Sounds like we need to find all the 5500 redline 8K tachs we can and gather some more info.

Tav