Physical size, the Windstar fans are almost a perfect fit to the "tall" truck radiators from the pictures and comments I've heard.
The Lx1 fans are made for a shorter radiator, (I'd suspect 3rd gens to be the same) although the width is pretty much right on. I've got a decent gap below my fans where the shroud ends and the radiator keeps going. More than likely due to the hood lines of the f-bodies.
In my case it works fine, but I have not been in 100* weather yet, and I don't have much that will increase the heat demands on the cooling system. Mild 355, no AC, manual trans, fairly light at 5000lbs. If I had AC and spent a lot of time in a hot climate, not moving fast, I'd look towards the windstar fans as a safer bet to offer good cooling.
Any electric fans can be wired up with the ECM controlling them, but I believe the Windstars have one fan that is high/low, and another that is at a fixed speed. I'd not spend time making the low work, I'd have the primary as high, and the secondary as low. Simplified wiring, and all the cooling. The ECM's also control the minimum on time of the fan, so whether it works on a high setting or low setting, the fan on time at a minimum will be the same. But you might as well cool it down faster.
Only benefit to running the low speed as primary is that demand from the charging system will be less, and you could get by with a smaller alternator more than likely. My 78 amp alternator handles the dual fans fine, but were it not for fuel injection forcing the idle at a set RPM, when the fan(s) kicked on, I'd have some serious idle problems. The load they put on the engine is incredible. They would actually stall the engine when they were coming on with ignition power. (part of the limp mode when my MAF was dead)
Even if you can get the 3rdgen fans cheap, if they end up in the end being inadequate, they still cost you money that you didn't need to spend. Not saying they won't work, just depends on your setup/application/location. You can never have too much cooling, only too little.