10 Inch Tonearms

Since a mono signal is entirely encoded in lateral motion of the stylus, one would think that maybe lateral compliance of the cartridge (not vertical) and inertial mass in the horizontal plane of the tonearm might be critical factors. Azimuth setting would just be for perpendicular physical orientation of the stylus; there is no such thing as crosstalk. Anti-skate is also less critical.

lewm, if you're going to add a tonearm to a modified Thorens TD160 for a Hana MC Mono, what arms would you consider? 

I would use one of the 5-6 tonearms I already own that are not already in use. Or if I needed extra length I’d buy a good one used, but only if the TT required the longer tonearm, not merely to enhance performance.

lewm, yes,absolutely do not want to buy new. I occasionally see Rega, Jelco and SME on the used market.