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5 to 6 inches is really high. You might want to consider having the spring re-arced if metal or replaced with a lower spring-rate fiberglass unit. You just ain't going to get there with an 8 " bolt. When I replaced my stock 9 leaf with the stock replacement the vendors sell, I had to go with a longer bolt to get a 2" gap at the top. The stock bolt is a 9/16ths with a 13 pitch IIRC but I went with a 5/8" x 9" which is more commonly available and cheaper. It required some drilling but made the attachment stronger than stock. I only used 8" of the bolt and cut the rest off. The end of the bolt is right at the botton of the rim so it's a tossup which hits first if I have a flat. A blow out with a longer bolt would make for a very bad day.