full traction shackles vs. others

I have the Full Traction 6" kit on my jeep and I'm wanting to put another inch or so on it and am looking at the tera flex 1.5" boost, but I am wondering what to do about the rear? How do I tell how much lift my shackles that came with the kit provide in comparison to the other companies out there without purchasing them? Is there a specific lenght of shackle that provides a certain lift amount? Anyone able to compare shackle lengths out there with aftermarkets? I'm wanting to find greaseable shackles that provide 1.5" more lift than the full traction kit provides. I'm toatlly lost about how to find that out. Thanks for the help.

think way outside the box. measure bolt hole to bolt hole on your shackle then get a shackle long enough to give you the lift ya want. call different companies or take it to your local welder. 1" longer shackle usually gives ya 1/2" lift

thanks. so if i had a 6 inch shackle and I wanted 1.5 inches of lift out of it, it'd need to be 9inches? seems like a huge shackle. is there a magic lenght that you shouldn't go over?