All my stuff was custom anyway....
Just about anywhere will work, they are made to be under the hood, but not right on exhaust manifolds...
, so anywhere away from the turbo, allowing the coil wire to reach (using as little as coil wire as possible) is good.
Dont skimp on electrical connections, only use the quality stuff.. no piggy back connectors, electrical tape and walmart connectors. Shrink wrap all connections.
It looks good, and you probaly wont ever have a problem with it.