Erick,
I built a very similar plane and you can see my post by searching "obscure russian bomber" in this forum. It is 75" span, 960 in sq wing area and just under 11#. It flys well with OS .52 FS engines. Based on the performance you probably get with the 120's in your existing planes, I would suggest moving up to the .70 or .80 range four strokes for your twin. With a twin you usually don't need two engines half the size of a comparable single; a little less will do. This is because the twin will have more propeller disk area and be a little more efficient.
Chuck