i have used chinese chinese intakes but they have to be checked for fitment first . if they are not square, you need to surface them or throw them in the trash.
your "builder" is also incompetent.
It was built by a bloke in the US Barn, Dynoflow race engines? Nevarda? ring a bell to you. It hydraulic locked on number 1 due leaking intake gasket, Chinese intake. None of the bolt holes lined up so it never would have come down square, may have been ok if even if they had run the next size drill down the holes, had no glue around the water way in the intake.
Had blown head gaskets, split the block spat the cam bearings out, had the wrong bolts holding the alloy heads down. It was just junk. Had a weird cam which was actaully an LS chev grind with less exhaust lift, so they put 1.7 rockers on the exhuast to try and fix it.
The 408 has the same gaskets as it happens but with Blackmax around the water way and a proper Edelbrock intake. By time you pay someone to square up a chow intake you may as well buy a real one.
If I was putting a 4 barrel on a 289/302 I'd put a Performer intake and a 570 Holley on it. Assuming you weren't planing on much else down the track. 570 uses the same throttle plate as a 450.
