Will an engine from a 1990 Camaro fit a 1995 Lumina?

My only concern is that they are mounted in different orentation, so the motor mounts might not line up.

no, the camaro engine has a distributor and is throttle body injected, where your lumina has a DIS ignition and is multiport injected. They are not the same and there are other issues that would make this swap not worth the trouble IF it could be made to work