OK, got a bunch of steering pictures uploading. Yours must be different, because there's no way mine has room for a full-round quad. There's a longitudinal 'bulkhead' for lack of a better word just aft of the rudderstock. This is what the backstay chainplate is bolted onto, so I'd be reluctant to cut it...
The pictures should give you a pretty good idea of my setup. Very dirty and neglected looking, but still...
Mine had some PVC pipes glassed to the underside of the cabin sole to direct scupper discharge (stupidly) to the opposite side through-hull. I had to remove these to make room for the relocated (and probably new) steering sheave box. It's a single cast assy with integrated steering stop. Can't remember if it's an edson
P/N or if I souurced a used Yacht Specialties part.
You can see where the pipes were run just at the back of the cabin sole, so I guess this is why the original sheaves were positioned too far forward. I remember them not leading fair when the helm was all the way over, but I do not clearly remember the original sutup.
In a few of the pictures, you can see where the sheave box has a big pin to act as a rudderstop, and rectangular/polygonal outlines inside the hull where the original rudder stop bosses were tabbed in.
And you can see my solution to the A/P steering arm. This arrangement has been in place for almost 15 years and steered the boat through some of the roughest weather (tropical storm in the gulfstream) that I would ever ask a A/P to steer in.
I'll post an album link in a little while when the uploads are done.