b4 you you tear the wall down brace both side of the existing wall with temporary walls to support the above weight while you rebuild. You can use the lumber for your pantry thats not built yet. Since the bearing wall is 2by6 your total width is going to be 5 1/2". This will allow you to put a three ply header at aprox. 4 3/4" using 3/4" strapping so that once it's finished it's flush with the esisting drywall. (you can nail the strapping later once header is installed) Nail this particular header in rows of 3 every 12" appart. Make sure the 3 2by10's are all crowned the same way with the crown up.(i suggest picking some relatively straight ones for this task) Your header will be supported by a tripple 2by6 at each end. Although this particular method may be overdoing it you can be assured that at least it's strong enough. Happy building!