I've got a 98 and I was just looking at a website where the 01 manifold dyno'd more hp's, would the 01 manifold fit on my 98

 

The ls6 intake will fit any ls1 engine but you will have to remove the egr system and $ for $ you can spend the money better in other places.eg:cam,cai,exhaust system,lt headers,under drive pulleys.The difference is the ls6 manifold has longer runners the the earlier manifold.

 

The runner length isn't the difference, in fact the runner length is identical on the LS6 and the LS1. The difference is in runner volume, and plenum volume.

Also, you don't have to delete the EGR system if you don't want to. There are plenty of modified LS6 intakes available from sponsors that have the EGR provision.