If I had it to do over I would get the bumper from the late 260z or the 76 280z and install them on my 77. They look better than the 77-78 ones. Then I would shave them getting them closer to the body. I like that look. There is a member here with that done IIRC.
John, it really depends on what you are wanting for rear bumpers. If your not convinced one way or another then wait til later. Dont jump just because the tank is out. Pulling the tank a second time will be easier because you will done it already.