flex is extremely weak. IMO, I think you could get more value at the WR spot for Bell. Even getting a WR for RB swap instead of a 2 for 1 trade would likely work out better for you, because you could get a more valuable WR. You're, essentially, trading an excellent RB for a couple of slightly above average WRs. I'd try to get some mid-level WRs from the FA market before I traded Bell.

If you do make the trade, it needs to include Bush. His value in PPRs is pretty high in that offense.