Summarized below is a quick summary of the polarization lines that will 
likely be of interest. Base on this I would recommend the tunning to be 
centered at 240 GHz. Only Zeeman molecules with strong coefficients are 
shown.

Clearly going to 350 GHz limits the choices for Zeeman 
polarization and also the number of suitable observing days per year.
The dust people would very likely argue with this assesment.

I'd go for best sensitivity and stability and worry about beam squint after 
the fact. It isn't unreasonable to expect that beam squint can be taken 
care of in the software, especially for the lines. Might be much harder 
for continuum.

Cheers,
Crystal

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Band 6  211 to 275 GHz.

Relevant Zeeman transitions:

CN (N=2-1) lines at ~226.33 GHz

SO (N=2-1) lines at ~236.45 GHz

CCH (N=3-2) lines at ~261.8 GHz


line linear polarization 

CO (2-1) line ~230.538 GHz


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Band 7 from 275 to 370

Relevant Zeeman transitions:

CCH (N=4-3)  349.107 GHz


line linear polarization 

CO (3-2) line  345.795 GHz