I have excellent bumpers on my 74 Z, eventhough the rear is painted, and I was told these things are expensive and hard to find. Is this true?

The answers to your questions are actually vague. The 74 through 77 bumpers are not being reproduced by anyone at the present time and may never be. The demand is not enough right now to justify the expense of tooling the stamping equipment to make them. The originals are solid aluminum that have been polished and anodized. The value is whatever the buyer is willing to pay for them. They are getting harder and harder to find because very few people kept those cars in good condition and alot of them were used as circle burners with the bumpers on. I bought my 75 20 years ago, the rear bumper had a slight bend in it on the right side. I was lucky enough to find a replacement in a salvage yard in 1996. The anodizing wears off like any other coating. Two years ago, I stripped, polished, and clear coated them. Although they are not technically correct they have yet to hurt me in any show. The rubber bumper strips are much harder to find in any kind of acceptable condition. Again, I was lucky that those were in almost perfect shape. Hope my rambling helped a little.

P.S. If your rear bumper is painted black it could be from a 77 Z or someone has painted it along the way.

The front one on the drivers side needs to be polished on the lower front where the previous owner stopped in the middle of the job, that area is about 6" long. Other than that they were kept polished and then he started the monochrome scheme. The rubber is perfect on both and I would say in a few hours the rear could be stripped and polished to the mirror finish that the front has, he only scuffed it with 600 grit paper.

It sounds like you are well on the way. I used 600, 1,000, 1,500 and 2,000 grit wet sand. I then used polishing compound with a flap wheel and stepped up to jeweler's rouge. Finally, I used a non wax based polish, washed them with soap and water and dryed them with a soft cotton cloth and clear coated them. After two years there have not been any problems.