I've been building camaros since day one and I don't know of any other stock type sector that fits. Have had some guys tell me they used the later model ones, but had some kind of ratio problems.
Any header is very close to the sector. some will fit and some will not, most will not. I gently massage the tube to get about a 1/4 inch clearance. I have even bolted them to another engine in the floor and sprung them enough to get some clearance. Good Luck
If you don't make mistakes. your not doing anything.
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