Actually, the Flex-a-lite died on me. The motor died. I was disappointed it didn't last any longer than it did. It's not like it sees a lot of moisture, etc here. But when it was alive, it performed extremely well. So I had a Mark VIII fan. I knew I couldn't use the Spal controller with it, so I built my own using relays, timers, speed controller, etc. Then the fun part was getting it mounted in a 99. First thing that had to happen was the radiator. Had to go to a 2000-2001 that utilizes the thinner (but much more efficient) radiator in the 5.0. I had to space the lower mounts a bit forward. I had to cut the threads off the water pump. That really concerned me as I didn't really know what would be left to hold on the pulley. But I shouldn't have been. Many miles into this and there has been absolutely no problem. I utilized a BMW temp switch that comes on at two different temps to control low and high speed. It's never seen high speed other than when I manually switch it. Darn thing really works well.
If I had it to do over again, I might try a fan from a 2004-2006 Mercedes CLK320/350. Those things are incredibly thin and...my God...you should see the air they can move. It is unbelievable when those things kick on to high. They are integrated with the controller, so a person would have to work around that somehow...but it's the most bang for the buck I have ever seen. I suspect they are thin enough to avoid a lot of the issues with the Mark VIII fan. I'm going to grab one and hang on to it for the next project.