I swapped in waggoneer springs on the front of my 75 FJ40 earlier this year. I have FJ55 rears in the back. If I were to do it again I'd wait until I could find a second pair of FJ55 rears to put in the front also.
The waggoneers I used were way too soft for my application. Granted, I still have the 2F, plus a winch and dual batteries, but the waggy springs went into negative arch and bottomed out onto the frame. I finally had to replace all but the top two leaves with my old cruiser springs. The waggys I found in a pic 'n pull easily supporting a '80 grand waggoneer with 127k mi. They appeared to be in good shape.
I also had to monkey around with the shims in the front spring hanger to eliminate a death wobble I picked up after the swap. The waggoneer springs are about a 1/4" inch narrower than the cruiser springs, so if you retain the stock hangers you have to shim the bushings. I had to adjust the shims several times until I got rid of the wobble. Probably not a big deal for a trail only rig, but I drive mine @ 70 mph on the freeway every day.
When I find another set of FJ55 rears, I'm replacing the waggy springs.
