Best way I've been able to lower stuff is to cut the tab off of the spindle and go higher on the spindle, or make a new one out of brass tubing or such. For the back end, leaf springs under the axle are easiest, just do as Billy said and make a lowering block. For spring over, make a cheapy spring under kit by putting the springs under the axle. Usually you'll have to make new springs out of styrene strip or brass strip. It isn't to bad. I've lowered a few mini trucks in real life, so if you have any questions few free to PM me.