HS shafts have a hard chrome surface because they use roller bearings in their rockers. I seem to recall rollers don't like plain steel shafts and non-roller rockers don't like hard chrome shafts. When I had those Isky rockers I used TRW shafts which were a stock replacement BUT are thicker and stronger with a polished finish. What you really want is a shaft that's going to stay round - unlike the stockers that went oval when you torqued them down. HS's are expensive. See if TRWs are still available or something like Hughes maybe.