Or, you could make your own like I did. Im using an Autometer Sportcomp. Cut and bent some stainless steel for the bracket (like Kenne Bell's), was quite simple.
Poston's doesnt mount on the hood, unless they came out with a new one recently that I am unaware of. it has a long braided line and you basically just lay it on the windshield. Its cool if you dont always want the gauge out, you can keep it under the hood. I used this one for awhile.