Just completed my modification, no chance to test yet. The mount is about 2 and a half years old and a little temperamental when guidied. Hopefully controling backlash etc will do the trick.
A couple of things.
When I tried to fit the idlers it turned out that neither hole was actually round. I just used a drill bit (manually) to gently 'round out' the holes. Using the 5.5 mm distance gap for the small pullies was a no go, it meant the lid (with spacer) would not fit. On the RA axis motor the pulleywent as far down as was possible, on dec it was a little higher, this in turn meant the large pullies were a little higher but no problem with that. It would seem to be issues with Skywatcher quality control and perhaps some minor differences in the motor parts used.
My mount is on a pier (tripod would have been a liability in the observatory), and I replaced the original saddle (useless thing) with an ADM dual saddle (bliss). So the HEQ5 is almost not an HEQ5 anymore. At least this mod and tuning worm backlash gave me a reason to use the handset. Polar scope - used it once.