[GONIF]

No offence to Josh and TSP ,but that "having to clearance" HAMMER TO FIT the headers is not something I find acceptable on a set of brand new headers in the 21st century . Most end users who install the headers them self would find that to be a problem. And most shops would first ask the customer if they would want the headers hammered /dimpled to fit B4 installing them .Back in the 60's this was some what more common and we had to do it sometimes on headers in the $60.00 price range Stainless Power headers are a great value ,and fit without a hammer. If you have good motor mounts and you need to Hammer To Fit then IMHO the headers are out of spec ,and the header manufacturer has a QC problem . If one brand fits without being hammered and another needs to be hammered on the same car ,then the headers are the problem . So while GM has it's own QC problems and it might be a GM QC problem ,the way to test this is to try to fit both brands on the same car and see where the fault lies . From the posts I have read ,this has been more often a TSP issue . Again I do not wish to disparage TSP ,but there are quite a number of people with fitment problems on here with TSP headers .