The rear spring mount on my 90 bronco is rusted and cracked and thus needs replaced asap. I am wondering what parts i will need to do this, and any suggestions on the easiest way to do it. thanks.

 

I haven't changed them on a 90 but on my 78 it was pretty easy. You'll want to get some good grade 8 bolts and nylock nuts to replace the rivets with, I usually end up changing the spring bolt also. You may want to replace the rubber bushing in the shackle.
I usually jack up both the frame and axle, frame first then axle just to take the weight off. Block both well. Loosen the spring bolt (the one holding the shackle to the hanger). Grind or burn the old rivet head off and tap them out with a hammer and punch. If the shackle bolt won't come loose burn it off but be carefull not to melt the rubber bushing. Tap whats left of the bolt out.
I like to clean and paint behind the new hanger before assembly. Then reasemble the way you took it apart. Antiseze on the shackle bolt can be your friend if you ever need to tear it back apart. Depending on how the gas tank sits you may need to drop it out of the way to get onto the nuts, or during disassembly, watch the sparks!!

 

Thanks for the input, about how long do you think this takes.

 

If you've got a nice place to work, all the tools, and things cooperate a couple hours.
If your like most of us and have to do it out in the weather with things fighting us (gas tank.....) I wouldn't say any more than 4. Unless things are really being a booger...