The mainspring will have extra pre-load equal to thickness of new steering bearing minus that of damper blade assembly if removed. Mainspring sag over time may mitigate this pre-load issue though. You could loosen bottom plate bolts and/or kingpin nut to allow articulation to fit mainspring and engage top oiler bolt. As a last resort spring compressors may help. Such situations are sometimes a balancing act.
Note the mainspring pre-load has no bearing (pun) on kingpin fixings since it sits between fixed upper and lower crosshead tubes.
