Okay, I'm putting my trader Howie cap on...
The 49ers are open to trading both of their 1st round picks (13 and 31). They have no picks in the 2nd, 3rd or 4th rounds. They do have 2 picks each in the 5th, 6th and 7th rounds.
I would trade 21, 53 (our 2nd) and next years 1st (which could be pretty late in the 1st round) plus Rasul Douglas. According to the current pick value chart the Eagles package would be worth from 1780 to 1900 points (depending where the 2021 1st lands assuming somewhere in the last 8 picks of the first round).
In return we get 13, 31, 156 (their 5th) and 217 (their 7th) worth 1781.2 points, so very fair trade
Then you go to the Browns, who have two 3rd round picks but no 5ths and you trade 31, 103 (our 3rd) and (168 our 5th) worth 711 points to the Browns for 41 (their 2nd) and 74 (their 3rd) worth 710 points.
So in essence we send picks 21, 53, 103, 168, Douglas and the 2021 first for picks 13, 41, 74, 156 and 217. So for the cost of the 2021 first rounder and Douglass, we move up in round 1 from 21 to 13, in round 2 from 53 to 41, in round 3 from pick 103 to 74 and in round 5 from 168 to 156 and add an early 7th round pick. Most importantly, it assures we get one of the top WRs. The only way this could go wrong is if the Eagles are terrible and end up with a high 1st round pick in 2021, but I don't see that happening.