The only belts which ever had offset guide blocks were the 35" for the 65-70-75-85-95 series.   All other widths were centered.  The blocks on the 35" were the same distance from the inside as 27" to fit the narrow frame tractors. 

Once you get a wide belted tractor slimed up, it is harder to work back out, but they don't slime up near as easily as one with narrow belts.  

The best way I have found to get one 'deslimed' is to kick dry dirt into the belts to dry out the slime.  Occasionally if you have really loose dirt you can do it by cutting kitties but usually it involves using your boots.   If you have clean water you can drive in, that will also do the job.