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Is there any reason I couldn't put a indicator in the platform and set a zero in the center of the bed and then use the same zero to set the three points in a circle for each tower. Then put the hotend back in heat everything up and then set my center z zero with feeler gage? If the platform is truly parallel to the bed then this should work correct? And the z should be the same at any point on the bed. Limits being the flatness of the build surface.

For bed leveling, yes this is fine. You will need to alter your firmwares zero position or you will crash the indicator into the bed. I suppose you could just leave the indicator suspended at a certain level and maintain that level throughout the process.