Hi guys, im in the process of fitting some hd cat cam valve springs in my 20v blacktop head, the new valve spring wont sit in the recces that is designed for the spring, they are 2mm wider then the oem spring. Looking around the net they all seem to be around 20-21mm wide. am i going to have to machine the head to accept the new springs? i couldn't find any info on the net so i'm going to assume i have the wrong ones!!

16V spring measure in at about 23.5mm, stock silvertop spring measure around 19mm