I have the N/A intake manifold. The 603N/A were never sold here so tough to find. So if you need an N/A find a used turbo motor remove the turbo, and the intake and exhaust manifolds and replace them with the N/A manifolds and you have an N/A. Should even make the 603 3.5 motor last longer.
As a bonus you'll get the piston squirters to keep think cooler. The 3.5 motor may not experience the ovaling of the pistons without the added pressure of the turbo. And even the #14 head of the 86, 87 3.0 ltr motor may last longer as well.