If I remember right the 208 crossmember is different, but don't quote me on that.
The 208 has a better gearing than the 205.
The 700 to 205 will require and adapter. MPG's on a 4x4 will be a little better if you have good gearing, but you are probably looking at 5mpg difference.
A 91-92 4L60 is a 700R4, they just changed the naming convention.