I purchased a extra rear caddy axle and I"am doing the change to move the Spring plates from the top side of the axle to the bottom of the axle.
I DIDN'T WANT THE OFFSET OF THE TIRES & WHEELS TO STICK OUT SO NO LOWERING PLATES FOR ME..
Put truck on stand's , you will need at least two jack's to lift the axle into position.
leave the springs attached to the truck unless you want to repaint or powder coat them
Loosen the U-Bolts and remove axle. Dont remove the center nut on the spring plate, Unless your going to powder coat or paint the springs.
With a 5/8 Cobalt bit aligned up with the hole already in the axle , Drill completely thru the axle and make sure it is straight and aligned.
This will hold the spring pin and will be the correct location for where the springs plates will be re-mounted.
Clean the Assy, take to a welding shop and weld three new beads around the spring plate, add another bead to the spring perch ( Why it only has two I dont know ? ) I paid a local dude 25.00
Repaint or Powder coat the axle Assy, I did satin black on all parts.
Always install new U-Bolts : 1/2 I.D. bolt x 3.00 I.D. x 5.-3/8 long
Stainless Steel U-Bolts are available for a little more $$ McmasterCarr.com
I found a set of M12 X 130 MM S/S bolts for the leaf Springs on Ebay U.K.
if you are looking for new bushings for the springs : VWDIESELCRAWLER, 130.00 per set of four ( poly )
Center Axle brake lines ( body to Axle ) Ebay : apex-tuning 90.00 set , Includes front lines also
You will need new shorter shocks :
Or Air Shock's Assy's ( Gabriel ) for 68 Corvette
P.S. I did complete satin black powder coat with a clear coat to keep all the springs and axle clean, the new S/S u-bolts and s/s brake lines & attaching hardware are a perfect upgrade..
Good Luck
Gee-Bee