Advice re those type 2 front air dams w/ bumper detail and matching rear

I've pretty much thrown in the towel regarding finding good used rubber bumper ends for my 76 280z 2+2 and new ones are just too pricey. For those that have done the conversion to the fiberglass air dams w/ bumper detail and matching rear one, do you have any installation instructions and experience you could share with me. For example, is there a lot of grinding of the fiberglass to make a good fit or do they come pretty well fitting? How do they connect (eg, bolt on somehow to the old bumper brackets or bond them on, etc) Taking the front bumper shocks off looks easy enough, but do I need to take the rear bumper shocks off to get them out of the way or can I collapse them? (I hate dropping gas tanks, sometimes having trouble getting the tank back up and in place).

Anyhow, if someone who has done this could take a minute and share with me how these install, I'd really appreciate it.

Thanks

Gary