is it hard to take dents out of a 71 bumper and how much will it cost to get it done>>before chroming

I think it may be difficult, bumpers are pretty thick. I talked to one guy that just got them as straight as he could, and put filler over them, and painted the bumper the same color of the car... It looked pretty good.

If you are going to get them rechromed anyway, don't worry about straightening the dents yourself. The bumper shop has the necessary equipment to remove the dents and return the bumpers to the proper shape and curvature. That's usually included in the cost of rechroming.

BEWARE of rechroming by bumper shops in San Antonio/South Texas. Some of them send their bumpers to Mexico for the actual rechroming. You may not get the best quality. Make sure you arrive at a clear understanding(written) of the warranty.