Yes there is away but its a lot of parts sourcing
First time poster i know but as a former owner of both bikes CX500 and CX650 i think i can add some basic info
1 there is no cush drive in the back end of these bikes its done in the transmission drive line with a cam and spring arrangement very robust set up and un-burstable.
2 There is a different drive collar that bolts to the rear between 500 and 650 but rather than models its actually years 1978 to 1982 Collar on wheel has an internal spline - 1983 to 1985 there is an external spline.
3 Here it gets complicated the 650 turbo has com star Disc brake rear wheel and the custom has a drum but if the opening poster can find a back end from a turbo he will actually gain disc brake capacity but from memory will need the swing arm itself unless he is capable of fabbing and welding the disc brake mounting to the swing arm.
4 then do the flat disc approach i actually have the cad models still i think from my set up and yes the discs are not finished after cutting out they need the the faces chamfered for the short spokes.
5 OR you get a rear wire wheel of a late model dirt bike make an adaptor to fit the drive hub and space it accordingly Spacer to rear wheel etc but you would still need to go disc brake
Its easier to go this way but you do need to measure accurate and machine accordingly remember there is no slots on the swing arm and it must pull through and clamp the wheel to the drive hub thats it.
But at the end of the day there is no right way or wrong way to go its what you can fiqure out hey mate
Good luck with it