Your 80's suburban springs are 3"?
Im using the 73-87 chevy front leafs, mine are 2.5" wide. With the bushings the springs are 3 1/2 inches wide.
If you want to use 2.5" chevy springs. Just destroy the bushings to get everything out of the ends. Order a set of greasable spring bushings with bolts from Off Road Design, also get the shackle bushing kit, might as well as get the shackle sides too.
Take and outside measurement of the shackle bushing kit, get the correct size DOM for that bushing, drill and sleeve the frame for shackle with newly aquired DOM.
For front hangers, take a chunk of 4"x .25"wall box tube, and cut out some front hangers, then weld to bottom of front crossmember.
You are free to look at my front hangers for the 73-87 chevy springs if you are ever near the north ogden area.