I do not know the measurement, but I would assume you can measure your coils to get the approximate amount of lift. If you get a chance, measure them and post it back here: someone will probably have the answer.
With 5.5 inches of lift I doubt you will be able to clear 40" tires. Not to mention that you are going to need to beef up your axles, drivelines, dana 20 output shaft, and basically everything else in the drive-train.
If you are only planning on using this as a street rig, you might be able to make 5.5 inches of lift work. You also might be able to get away with 40"s without having to do a whole lot of work to the drive-train: just drive with a very light foot. If you do go 40"s, you should probably upgrade at least the brakes and ring and pinion gears: what year bronco is it? A later model with a 44 will hold up much better then an early model with a 30. Either way, I think 40s will definentally be a little much for a stock drive-train on anything other then pavement.