The road off of Hwy 39 [North of Ollokot] to Imnaha is USFS road 3955...dirt and great ride down the canyon...not difficult with lots of ranches along the way...look for small sign on right [N] side of Hwy 39 for turn-off.
Sorry, seems you want direction out of Imnaha SB to Hwy 39....3955 is the only road in 'town' that goes SB...right side of road between the two buildings and across from Post Office [North side of road] just across the bridge when coming into Imnaha from Joesph...it continues SB to intersect with Hwy 39 described above..
Phil