1. Buy a fuel pressure gauge and check it. If it'* out of spec, replace the pump and/or FPR.
2. Remove your exhaust manifolds and inspect for cracks. You have them. We all do/did. I strongly suggest porting them at the same time.
3. BUY a scantool. You'll need to scan now for KR and periodically through the hotter months.
4. NEVER run anything but 91 octane or higher. Consider a higher octane with the smaller pulley if it'* available.
Failure to abide by these guidliness can spell doom and BOOM for you. And it has in the past for a couple people. These cars are getting older, and these things need to be repaired BEFORE doing any pulley changing. SC pulleys are not a magic mod on any L67. Supporting mods must be done first.