Is there a trick to WD head stack alignment?

I am still relatively new to disassembling disks. As a self teaching lesson I have disassembled, removed the heads and reinstalled the same heads in several drives. Currently I am working on what was a fully functional WD1200. Every time I reassemble a drive it continues to knock. Obviously the heads are not correctly aligned. I have tried magnet shifting, HDA shifting through a lever (joystick?) assembly screwed into the top screw. But no luck. Is the alignment so critical that I will never be able to get such drives to align. Should I give up on head transplants or do you just have to spend hours shifting things until it happens? What are the indications that you are getting close?