@terrible , if the vinyl is not perfectly flat the tonearm might wander back and forth a little. As long as the net motion is towards the spindle you are in business. If it does not head in one direction or the other dial a little less anti skate.
As for what to put on the SME 12A, that could be a long list. The Windfeld Ti is a great cartridge. Some would even say as good as it gets. The Lyra Kleos would do very well. The Soundsmith Paua would be another. Grado Statement 3. Clearaudio Stradivari. Dynavector Te Kaitora Rua. My Sonic Lab Eminent EX and I am sure a lot of others.