The reason you were told that it would look proportionally weird is that pre '93 rangers had smaller wheel wells. Therefore, requiring more lift to fit the same tire size as a '93 on up truck. I have 33's on my 93 Ranger with only 2" lift.
You can fit 31's on a 93+ Ranger with no problems at all stock. Hell, alot of newer Rangers come FROM THE FACTORY with 31's.
31's and a 4" lift would look odd to say the least.
Here's my truck with the ~2" lift ( probably closer to 2.5" rear, and 1.5" front) with 33x12.5x15's on it.
I can get you a better picture if you want.
Just think of that, with more lift, and smaller tires, it isn't going to look good.
That is my opinion though. I would say slap 31's on it the way it is, or do the lift and put on some 33's.