Yeah, skip the add-a-leaf idea altogether! They will sag after a relatively short time depending on how much you wheel and flex her.
Personally, building your own rear pack is inexpensive, (the local pick and pull here sell full leaf packs for $12.50 each, I mean c'mon.) and much more reliable than the other options. Then all you have to do is buy the springs for the front. Easy.
Oh, and don't throw anything out until you've got it just the way you want it.