Lee,
never been done the OAG trail, but most that have either swear by it, or at it, most at it.
I have always used a separate guidescope, and on my newt it sits on top, but in your case, you have to muck about with things, so another option could be better. On top, you will need a couple of radius blocks, and a mount the guidescope rings on these, or get rings with a curved base that fit your existing tube rings. Either way the guidescope rings need to allow plenaty of adjustment for locating a suitable guidestar.
With some of my other scopes I use a side by side arrangement, home made and Losmandy call it a "DSBS". Both have their merits, and drawbacks. Need some pictures, get me at
g.beal@xtra.co.nz
Gary