Any cartridge recommendations for a Grace G-707 arm on a Thorens TD-125 deck?

The Grado Opus 3 would be a good match!

Grado Timbre Series, Opus3 - The Absolute Sound

Ortofon Super OM 30 would be an excellent compliance match.

I think you could find an F9E or Ruby with a little patience. Then get the SoundSmith prefab stylus assembly with sapphire cantilever and CL stylus.

Thank you all for taking the time to provide such helpful responses. I've already begun researching them.

While I have your attention - so to speak - do you have any thoughts on a good - but affordable - tube phone preamp to plug this rig into a Parasound P7 and A21 and then Magnepan speakers. There are a lot of good-looking preamps out there so opinions on good options would be welcome.

Denon DL-301 mkII is very good on that arm.

@fusian  Great recommendation!