I have had 4 different sets of wheels on my car. I had 18s that required spacers/adapters, and my current 16" wheels do as well. I am not the biggest expert on the planet, but I have done my fair share of messing around with wheels on Buicks, and making wheels fit that normally would not.
Let me give my opinion. Yes, the half inch spacer would technically make the wheel more like a wheel with 4.75" backspacing. There are a handful of guys who have gotten away with 4.75. The real issue here is the width of the tire. You might get the rim alone to fit, but if you want to run even wider tires, that's where your rubbing is going to come in. Tires like M/T streets have pretty bulgy sidewalls and that can cause problems.
Worst case scenario, buy the wheels and tires, start out with a .5" spacer, and see if it rubs. You have to REMOVE the wheels and actually look for signs of rubbing, it's not always severe enough to hear it. If it is rubbing the frame or quarter panel, there will be a very obvious "clean" spot. Rubbing on the body is easily corrected, you can roll the inside lip of the fender, or run air bags and keep the rear of the car lifted up a little bit. Rubbing the frame is harder to correct because your only options are notching the frame, or spacing the wheel out even further.