Does anyone know where the rectangular opening located below the intake ports on a 89 center iron housing goes to?  I am looking to drill and tap for 10-32 in this area to hold a plate that will secure the slide throttle to the engine.  The intake ports are not used and there are 2 existing tapped holes that would secure a cover to block off the ports.  Don't want to drill into a water passage.  Thanks for any help.

Joe Berki
13b P Port