I jumped on a killer deal on a GSO 2-speed linear bearing focuser. It was secondhand, but unused - it came off a GSO R/C scope.
The retaining collar on the GSO focuser is the same M90x1.0 thread on the end of the C80ED tube. The focuser flange doesn't match the ID of the OTA, but if you found something to act as a filler gasket (O-ring or even plastic plumbing gasket), this would not require any adapters to mount to the tube, and would simply bolt on.
In addition, the GSO focuser is a bit more than an inch shorter than the stock focuser, so you would make your scope instantly binoviewer friendly without (the apparently horrendously offensive and sinful act of) shortening the tube.
However, since I already had committed said crime, and wanted proper focuser spacing, I machined an adapter to both make up the additional length, and mate exactly to the mounting flange of the GSO focuser. I also plan on mounting a Vixen-style finder bracket to the flange.
The drawtube travel of the new focuser is quite a bit shorter than the stock focuser, so I also made an extension tube for mono-viewing and imaging.
The new focuser is a HUGE upgrade to the stock focuser (obviously). No backlash, no image shift, and precise focusing. With the old focuser, the drawtube would tilt easily, affecting collimation. Now collimation is perfect, even with heavy binoviewers hanging off barlows and extension tubes.