recently replaced engine and gas gauge and speedometer not working .any help?thanks

Check the wiring connections on the harness if you took it out.

Some have issues with the wiring in the cluster needing a reseat of the harness.

The speedo could be a connector on the transmission. However the fuel gauge wiring runs under the carpeting inside the car and goes out under the passenger side of the back seat. That doesn't make much sense.

Looks like the cluster connection may be your best first thing to try.