Some places offer a mono to multi-leaf adapter for these cars which will simplify the install by providing the correct hardware, spring pads, spacers etc. Make sure that the adapter fits your spring pack. There are 3 leaf, 5 leaf and possibly other kits available. If the kit doesn't match the thickness of your spring pack, it wont be much help. You can also assemble your own kit, but it may take a few trips to hardware stores to find everything.
I didn't triple check when I bought my kit and it was for 5 leafs. The listing didn't mention how many leafs it was for. I ended up making a few trips to the hardware store before I was done to get it all to work.
Thicker springs will require longer bolts or U bolts for mounting the springs to the rear end.
When using U bolts be careful and don't kink the brake lines when you have to move them out of the way to put the U bolts around the rear end. Also the U bolts may be 1 size bigger than the T bolts, the holes in the plate and rear end mounts may need to be opened one size.
New spring pads need to be the right ones. The first set of pads I got were too wide and the built in steel centering washer was going to interfere. Maybe they were bottom spring pads, but they wouldn't work as uppers. My Chevy II does not use a centering bolt on top of the springs. The mounting kit I bought had the stockstyle pads that fit the upper mount. I did not use pads on the bottom with 3 leafs. My kit also did not use a spring pad on the bottom. My assembly manual states the lower pads were not used on wagons & F40 springs. I believe these were stock style multileaf.
Bolting up the lower mount and springs. In the end I ended using standard grade 8 bolts.
Note these mounting bolts are one size bigger than stock since I had opened the holes for U bolts originally. To get a wrench on the head of these bolts on the upper mount one of two things need to be done. Use Allen wrench bolts with washers. You can't get a wrench on these bolt heads when in the channel of the mount. Maybe that is why stock used "T" bolts. The other option is use a spacer to move the bolt heads up to allow getting a wrench on them. Even with spacers from the kit to make the heads accessible, I had to file a little clearance on the wrench to get it to work.
Mono leafs didn't have spacers between the upper and lower mount. With multi-leafs spacers between the upper and lower mount assure the lower mount is even side to side and front to back. So you don't bend the lower mount.
For spacers between the upper and lower mount I used SME washers for spacers.
The multi-leaf kit I
bought was for 5 leaf springs and the spacer was too thick for the spring
Having multiple washers
per bolt that want to slide off and getting the lower mount plate up, and
all 4 bolts thru, bushing in the lower mount hole and 2 nuts started is 90%
of the work.
If the spacers between the upper and lower mounts are too wide, the spring will not be held tightly and this will cause major problems sooner or later. Make sure the spring is held correctly.Problems I had with Lock Nuts.