90 Camry, speedo

Speedo and tach off? Did you put 4 cyl in a 6 cylinder car? Or other way around? 6 cyl have 15" tire and 4 cyl have 14". So you could buy new tires the same diameter as donor for gauges. A resistor might get the tach more in line. Or simply get one from car with matching engine.

There is no adjustment. Speedometer sending unit in the transmission, sends out four impulses for each revolution of the driven gear. I'm with Wolfgang. Sounds like the six cylinder speedomter went in the four cylnder car or the other way around.