Will the 7576 intake fit a stock 318 with stock 318 heads

Yes; RTV only.
Sometimes there is not enough room, and the cork seals may split. and
usually, they make the manifold sit too high to get the bolts started. and if you start fidgeting with the intake, the gaskets may slip out of place.
It's just easier to RTV the china walls.
But, as mentioned, don't forget to pull the dowels out of the china walls else they may keep the aftermarket manifold from dropping down, just like the fat cork endseals do.
As to the RTV, tho
you gotta make sure to put on the right amount, and as for me, I always put RTV on BOTH the wall and the intake. Then I assume it's stuck on both.
If you screw up and it doesn't seal, and you don't discover this until after the RTV has cured, it get's frustrating.