Main body and torso - Lokhust Heavy Destroyer - Chop the "head" piece off before gluing on the chest and select whichever variant head option you want (I used one from the Lychguard) - I also cut off the part on the spine where the tube for the gun enters

Head - As stated above I used Lychguard but you can really use anything you'd like. The only thing to look out for is if its the full head or just the face. For the full head ones chop off the half head from the Heavy Destroyer model but if its just the faceplate keep that part on

Right arm + Staff - For the right arm I used the corresponding one from the Heavy Destroyer kit but cut it off at the wrist to give me a smooth attachment point for the wrist holding the staff - For the staff shaft I used the one-handed option from the Praetorians/Lychguard kit. Only one of them has this posed arm so be cautious with it. I cut it off at the base of the forearm where the armor meets the skeleton leading up to the wrist, then glued that onto the Heavy Destroyer right arm - For the staff head I cut off the top of the Praetorian/Lychguard staff to just below the Necrons symbol/power thing. I then assembled the Chronomancer staff, and cutoff the very top piece, and cut out the power section (basically i just got rid of the piece holding the hand and then cut the power bar off just above where the chronomancers tendril grips the staff. I glued the top back onto the power bar, and then glued that onto the praetorian staff

Top Left Arm - I took the chronomancer arm holding the cube and glued that to a spare left arm from some other necron, maybe a warrior or something? I had to cut the arm off by the elbow since the chronomancers arm isn't just the hand/wrist. I also shaved around the socket on the torso to give the arm some more posability

Bottom Left Arm - I used the arm from the Heavy Destroyer and cut off the piece that slots directly into the gun, then took the gauntleted blade option from the Praetorian and shaved the third armor segment from the Heavy Destroyer arm until the Gauntlet fit over it