In the front, get 4 pieces of 2x4 rect. tubing 4 inches long. There are 3 bolts holding the front of the springs to the axle and 3 holding the rear of the springs to the body. You drill 6 holes in each piece of tubing. 3 on the top and 3 on the bottom. Off set them all by 1 inch so you will end up moving the front axle 2 inch's forward when you put the blocks between the spring and the body and the spring and the axle. On the rear of the spring mount there are spring locater mounts welded on. Just put the blocks on top of them and bolt them down. Leave everything loose, find a spot to measure to and center the axle, then tighten it all up.
In the back, get 2 pieces of pipe with an I.D. that will fit over the spring locater pin. Have them cut to 4 inches each. Jack the cart up and place these on the locater pin. Get 2 pieces of pipe that have an O.D. that will permit them to slide into the fore mentioned pipe. Cut these to 4 inches and slip them into the other pipes. These will locate your springs. Slip the coil spring on and you will have a 4 inch lift.
You will have to get off set rims if you get tires bigger than 20 inch. The bigger tires bulge out and will rub on the inside if you do not have off set rims. Maybe the 20 inch will do this too. I do not know.