Yeah the inliners site is great.
Stock 250 intakes have holes on the bottom of them, but it look's like a water jacket, like the Clifford intakes. Here a pic of my spare one. You won't hurt your intake valves with this exposed and you won't be sucking air with a vacuum leak. With the headers, you will be getting rid of the exhaust leak in the stock manifold.
You can bulld a makeshift heat riser that won't be as good as OEM but it will do a little in the winter. It will not plumb gases into the intake like PVC, just around the intake like a warm little blanket
