Well I got a hold of the MSA holley clifford intake and mine was a 75 and it was fuel injected. I don't know a lot about the 260zs but with mine the pump wouldn't work with the wiring harness anymore, because of the fuel injection. Anyways I don't really know what to say just run all the basics like fuel pressure, fuel pump, fuel lines, sorry if you have already done everything just suggesting maybe double check? i know that can't hurt. Hope i could help some.