I don't know about 75 or 76 but my 74 had 5 mile an hour shock bumper brackets. I swapped them out for 73 brackets and then worked fine. 74 may have been an odd ball year, idk, but mine had holes in frame for either one if I remember correctly. At least I no I didn't have to to drill any new holes . Hope this helps!
I have a '74 that does not have the shock bumper in the front, but has it in the back. It came factory like this! I want to replace my front bumper on my '76 with something similar, and lighter :)