So, the way I did it was a GL500 swingarm heavily modified, with a custom driveshaft (front part of CX500 shaft and rear part of GL500 shaft). With the GL500 swingarm and linkage setup, a Hayabusa shock was absolutely perfect. Perfect travel, perfect spring, perfect damping, for a 220lb rider and a 110 lb pillion. Using a Hayabusa shock will require heavy modification of the GL500 lower shock mount, as the GL500 has a (very wide) clevis, and the Hayabusa shock has a clevis. I've used a 09-11 GSXR1000 rear shock, which has eyes on both ends, and that works too, but the spring rate is a softer and it has less travel. Still doable, especially if you're lighter or always riding solo.
I have no experience with monoshock mounts that just welds a shock mount to the swingarm and rear frame tube. I'd look for a bike that does it that way, and use the shock from that. There are kits all over eBay to give you that kind of setup, but I have no idea what shocks people are using with them. I do know the Hayabusa shock with a GL500 swingarm and associated linkagery gives an absolutely amazing ride. The suspension is the absolute best part of my 650 street scrambler. I daresay the rear is better than the front, and the front is really good.
Note that by going with the GL500 swingarm you're extending the wheelbase about 2 inches (hence the need for the custom driveshaft).