I've used the IPD headers for my 68-142 and 73-145. They kick in a little late compared to the v-perf header but definitely better than the cast iron. The 73's header cracked at the collector box so I got the v-perf stage one unpainted (no salty roads in Oregon). Installer said he had to build up one side of the header bolt washers and there was a contact rattle until new engine mounts went in. Installer said he could put on a new collector box to the old IPD header so I'm holding that in reserve. IPD says they have a new mfg (Pertronix?)as supplier so maybe design is different. IIRC John Parker said that a header usually lasts about 7-8 years when I commented about the significant weight difference