For best fuel delivery performance the centerline of the thank should be level with the spray bar or jet (needle valve if you will) not neccessarily the center line of the engine.

It is important to set the tank on a level as indicated by this relationship. It is not neccessary to run the tank brass or alum tubes throught the firewall, instead keep them short and just run the fuel lines throught the old holes or make new holes wherever they need to be.

Tanks that have the whole cap and rubber bung that fits tightly into a large firewall hole are a very poor idea and should not used in such a way. Think about it, we go to all the trouble of packing the tank in foam rubber to prevent foaming then sticking the hard cap directly into a hole in the firewall. Makes the trouble of foam packing the tank completely pointless.

John