I would not do 40 on an aluminum intake. Cast iron ok, but not aluminum. I believe I torque my aluminum manifolds with a good washer to 35 ft lbs. That should be adequate for a grade 5 bolt.

67 Coronet 500 9.610 @ 139.20 mph
67 Coronet 500 (street car) 14.82 @ 94 mph
69 GTX (clone) - build in progress......