Only way to tell is to see pics of him at 170 and go from there. Im speaking of bodybuilding stage conditioning of course. I think with a nice ec stack he could get there in about a month (155ish)
since he is not training for something...I would recommend the gradual decline in weight..you are suggesting a 30 - 35lb drop in 1 month..
I am the same weight as him but I carry my fat very different from him...I can see the benefit of droping 2lb per week
cleaning up his diet..dropping carbs to PWO only