Starter not disengaging

[NorCalC20LWB]

Rebuilt my 350 w/HEI and am now working the bugs out, first time experience for me so there are a few. The starter began to stay engaged even with the key out, so I replaced the ignition switch first, no difference. Figured it must be something in the starter/solenoid then so took the opportunity to upgrade to a mini starter, should be here today or tomorrow. After taking the solenoid apart it appears the contact points have been arcing together. I did screw up when replacing the headers and forgot to take off the battery negative cable and got some decent sparks when the wrench touched the positive lead on the solenoid and the engine block. Would this have caused the problem? Want to make sure I don't run into the same issue after replacing the starter.

As always, thanks for any help!

Brian