You'll have to pull the intake and put a helicoil in it.
If you can't do it, take it to a shop and get it done.
some engines have the block and deck milled and that moves the head intake flange away a little bit from the manifold.
When this happens the intake will sit low, and the intake will ride down on the bolts. Usually the end bolt holes on the intake are smaller than the others to locate the manifold.
Pull the end bolts and see if the manifold is low enough to hit the bolt threads.
If it is, you may need to use thick manifold gaskets.
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer