try Z-SPECIALTIES he has a huge assortment of all z car parts new and used . www.zspecialties.com . this guy really knows z cars and has helped me out a bunch over the years .
there was a episode on the history channel a few years back that gave the entire history of the z car and the changes made year by year . you might want to see if you can get it .
I have a 71 240z that has no bumpers and i have only beenstopped once. i ended up mounting two pieces of flat iron stock about 1/4 thick to the back on each side. it sticks out about two inches. its looks kind of like > on the back. i painted them to match the car and they look great . its cheap and simple to make and really looks good . i made one for each side and they are about 14 inches long . i will try and find a pic i can send you .