Be carefull with thinking the Datsun Spirit brackets will bolt up right.
I bought the 240Z to 280Z rear bumper mounting brackets from Datsun Spirit. Technically, the brackets are for European 260Z/Japanese A-S30/S31 models. These brackets bolt to the mounting holes in the valance just like a 240Z bumper would. Unfortunately they don't exactly line up with the MSA bumper mounting brackets. I had to make new brackets for the MSA rear bumper. I used a Dremel to cut off the MSA brackets, found some steel at Home Depot in the decking bracket section the same thickness as the MSA ones, bent them in a Z shape at both ends and then glassed them in. The brackets are short enough so the bumper sits only about 1/2" from the rear valance panel. The 240Z mounting tabs on the bumper are too far forward to use unless you drill through the fender on the 280Z. Since the 280Z fender is a double wall fender/inner fender I decided to use the stock 280Z fender mounting nut which is about 8" toward the rear from the 240Z tab. The 280Z mounting nut does sit below the bumper a little but not much. I made new the fender mount side tabs and glassed them in after cutting out the 240Z tabs. I put a piece of 1/8" rubber under the tabs to protect the body. Even though the Datsun Spirit brackets didn't fit perfectly I'm glad I didn't attempt to make them. It could be done but would have been a major effort with the equipment I have. The MSA 240 bumper is supposed to be an early 240, I don't think the Datsun Spirit brackets were designed to fit the early 240 models. Rather than try to modify the Datsun Spirt bracket I made new bumper brackets, it was easier for me. BTW when I talked to Datsun Spirit last October he was almost out of those brackets so you might check with them before ordering.