L98 heads are angle plug heads (with the exhaust floor raised I believe a 1/10"). As a result of the angle plugs, most headers will not fit. However, I know Sanders (I believe out in the SF area) makes headers and performance manifolds for the G body with angle plug heads. However, I am cheap and I am running LT1 exhaust manifolds on my L98 heads. L98 heads can be gotten from Camaro, Buick, Cadillac with LT1 engine. These LT1 exhaust manifolds are supposed to flow pretty good. I will see if I can scare up a picture of my LT1 exhaust manifolds.