Dave:

My SL-1 had the same hatch on the bottom of the fuse. I used this access hatch to install one of the MK bellcranks that allowed me to drive both elevator halves with single servo. This bellcrank allowed me to install the elev. servo forward in the fuse near the wing TE. I also collocated the rudder servo next to the elevator servo. I opted not to install the servos in the rear of the fuse for balance reasons. I really believe it is an SL-1.

Ed