[IndyBowtie]

Dan
I was in a similar dilemma (and have the same name). Ran my Fatman front MII for 4 years with springs, and stock rear springs in back, with a few stiff leaves removed. I tow vintage campers and the rear was awful soft so I installed air shocks, but still didn't like the ride. Decided to 4 link it, and bought a kit that included air bags for the rear (TCI). Probly could have just got by with Schrader valves, but then opted for a tank, valves, lines and compressor system from a local merchant ( not an AccuAir). I spent a ton on the parts as it was, but if you want to spend the extra for AccuAir that's your decision.
Well, before I even got it back on the road, decided to convert the front to bags as well. Fatman makes a neat conversion kit to do so. Of course more$$$.
Now...I am not laying the boards. No frame notch, or center cross member and cab notch. Aired out the boards are 4-5" off the ground. That's with urethane bump stops contacting the axle so the frame doesn't . At best bag pressure for ride the boards are 7 1/2" off the ground. I think am will happy with it. Can't answer the question of bags and springs, but a lot of dudes I talked to suggested against it.
Regards
Dan Sutton