Is it OK to attach the ground wire to the power terminal (where blue wire attaches) to chassie instead of fuel outlet tube to fuel line? Any advantages? Car is a 69 GTX.

Sounds to me like you are creating a dead short. You can ground it to the chassis but not from the power terminal. It's easier to do it the factory way. If you want to do it without the factory strap then two fuel line clamps and a piece of wire will work.

I drilled and bolted a 1/4 blade terminal to the fuel sender and ran a wire from it to body ground. make sure you seal the bolt hole. This was on a 69 superbee tank and sender.