I alternated using the neutral and ground bus for the pigtails to increase the effective wire gauge...
No, no I didn’t do that, yes, I know what I was doing. :)
Having to wire both hot and neutral to the same breaker is what took this project so long. The original installers, not thinking at all about future code requirements, moved all of the neutrals to the right side bus bar, and I had circuits coming in from above and below, leaving me essentially with a rats nest to untangle 1 breaker at a time. I had to disconnect 1 hot wire, and trace it back all the way to the incoming Romex, which were all clustered together. It took me about 6 minutes per breaker instead of say 2, or abour 4 hours for 20. Once I realized that I was better off pulling all the neutrals at once things got a little easier.