the difference between the 1-piece and the enhanced design is that the 1-piece is just that, the upper control arm is like your standard upper control arm of most vehicles, it is one piece that goes from one mounting point-to the balljoint-to the other mounting point. This is on the driver's side(stock)
The Enhanced design is on the passenger side and it is two pieces. there's the piece that attaches to the frame, and another piece that attaches to that (this has the balljoint in it). The Enhanced design is one of Ford 'wonderful' design ideas to help solve caster/camber problem in our trucks.
I'd get the MOOG enhanced design for BOTH sides. That way you have a removeable/replaceable balljoint, AND can get the caster/camber adjustment even better.
OR go with Camburg, Fabtech, or some other company that specializes in offroad/prerunner setups. I know Fabtech has upper control arms, and lift spindles for the Edge series trucks.
2001 Chrome Yellow Edge 2WD Reg Cab 4.0 SOHC