DL1000 and DL650 share the frame, only difference are the engine mounts, which bolt on to the frame...
That means fitting the 1000cc engine into the DL650 if a piece of cake, if you get the DL1000 engine mounts. Getting everything to work will be a PITA, as you basically need the wiring harness and ECU of the SV1K on the DL, and the wiring harness will need a lot of work to fit.
As fof the issue at hand, it's quite common for the 650s to burn oil as they get older, valve guides wear. If you're replacing the cam chains, don't skim and replace the cam chain guides too!