My First step is alway gather some good information: what was used in the studio?
Everyone is ok with the fact that there is Chorus and Reverb (obviously included in every preset mentioned here!), and that it is a clean channel pushed to the limit of the volume.
Either the famous Marshall JMP 1959T Super Lead or some unnamed Fender "tweed".
My starting point was testing the various British. There is a problem. Fender did not put a Britsh Clean channel in the mustang. I used what i have: very low gain but with all the volumes cranked. I dont like this very much, but that's all you can do without a british clean tone. I tried the different 4x12 cab model and i found that the greenback have the right degree of frequence separation for the clean suff.
To my taste the better solution was to tweak my trusty Fender 57 De luxe model, emulating the maxed volume with that bit of gain to compress the sound. I keep the default cab that was just so good to me. Maybe the British 70 was the best matching tone, but using the F57DL allowed me to have a more versatile tone, that works better with the neck pickup and allow me a cleaner sound with the volume pot. Overall a preset that really deserve his slot on the amp.
I will update later with link to the 3 presets i made!