How does ModuleGimbal work?

[Deltac]

I'm trying to programatically change the gimbal of an Engine to point at the center of mass, however ModuleGimbal is throwing me for a loop.

So far I can't rotate the gimbal transform by itself (though I can rotate the thrust transform, however that doesn't produce a visual effect).  I have to change initRots, but I can't figure out what initRots is supposed to be.  In the MainSail engine, the initRots starts off as 0,180,0, but in the new poodle, it's 0,90,0. 

so I don't know what math I'm supposed to do to set the initrots.  (or perhaps there's a better method?)