Obviously you'd like the selected cartridge to fit the headshell. Just remember this is a low mass arm so higher compliance cartridges should work best. Popular choices were Grado, Shure, Pickering, ADC, etc. Lots of choices new, and with a little luck a NOS or low hour used cartridge will be found. I'm not familiar with the Ortofon 2M.
I read about replacing the arm tube with a Technics recently as well. But since you've already done wiring and bearing upgrades all that might be gained is accepting a universal headshell, unlike the AR.
If your arm still has the damping pin that should be removed. AR recommended doing so and I understand eliminated it in later production. Fairly simple and instructions are on line.
Lastly I just saw mention that 3-D printed headshells are now offered, maybe on flee-bay. Original ARs are a bit expensive.
I read about replacing the arm tube with a Technics recently as well. But since you've already done wiring and bearing upgrades all that might be gained is accepting a universal headshell, unlike the AR.
If your arm still has the damping pin that should be removed. AR recommended doing so and I understand eliminated it in later production. Fairly simple and instructions are on line.
Lastly I just saw mention that 3-D printed headshells are now offered, maybe on flee-bay. Original ARs are a bit expensive.