'67 GTO LS3 Swap

[rockytopper]

You should have no issues using the stock tank without a evap system. I have had no issues with the ls1 I'm running with with the same setup as you have out lined. Be aware also some of the oil pans have clearance isuues with the tie rod ends. I run the modified f-body pan from s&p which has notches in the front corners to clear the tie rods and they barely clear in my case. It all depends on your motor mounts etc.. The f-body manifolds work with your A-body if you donot want to run headers.