The GT40 lower will not match up to the stock upper.
The Holley Systemax I intake is not actually a ported lower, it is in fact a modified design. Basically, it has straighter intake runners than the stock lower. The complete Systemax I kit consists of this lower, a Lunati cam, and a new timing chain. Holley claims 271hp @ 5100rpm, and 328 ft/lbs @ 2900rpm. The lower intake is available seperately as a special order item.
The Cobra and GT-40 share the same lower intake. Personally, I consider the Cobra a better choice, since it's upper intake can be ported, while the GT-40 cannot.
Installing a cam will require lifting the engine, or removing the front end and radiator, so you can slide the cams in and out of the block.
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Moxie Racing