Shimano GRX parts compatibility with XT or XTR FD on Salsa Fargo. (BSA73)
The Salsa website states for the 148mm rear spacing you need one of these adapters to mount a direct mount front derailleur Problem Solvers FS1328

Source: Salsa Fargo 2019 Spec

I don't think you'll have any problems with those shifters and front mech.