>>1620370A yee lmao, that rear derailleur is kind of distinctive
>>1620372six speed over lock nut distance is 126 mm
for 7 speed the over lock nut distance is 130 mm
for 7 to 9 speed the over lock nut distance is 135 mm
but given the Trek 850s approx age of 1995 and it not being a bottom of the barrel bike shaped object the over lock nut distance should be 130 mm anyway
with steel frames its possible to cold bend the rear forks to be a little wider
but alignment can be a problem, I would not say its easy or safe to do
https://www.parktool.com/product/frame-and-fork-end-alignment-gauge-set-ffg-2 