1949 Dodge B1D Sending Unit Locking Ring Tool

[JimmyJustice]

I have a 1949 Dodge B1D truck that is need of a new sending unit.  The hole in the floor board lines up (generally) over with the sending unit, which is on top of the fuel tank.  My problem that is need of a solution is this: 

 

The angle between the opening in the floor and the sending unit is too steep for me to get a screw driver flat enough to move the locking ring.  The sending unit is within a recess on top of the tank so I cannot get to it from underneath between the floor and top of the tank.  The inside dimension of the hole is 2.75 inches, the locking ring is roughly 2.5 inches below the hole and the three slots on the locking ring to tighten/loosen it are roughly 2.25 inches apart. 

 

Question:  Is there a specific tool for this application, and if so where can I get it?  I have searched the interweb and local auto stores and cannot find a tool that would work in this situation.  Any suggestions or helpful hints are greatly appreciated.  (I'll also posted this in the Technical forum)

Jim