How do I replace rear leaf springs? '93 F150 2wd 300cid I6?

I have purchased new leaf springs, shackles & brackets. I won't have a problem replacing the brackets. But I'm wondering what will happen when I try to force a fresh new leaf spring into the same position as the old tired sacked-out leaf springs. Will I have to jack the truck up very high to get the axle to drop low enough (to account for the stiff new arch in the new spings?) I've already sprayed a oil on all the nuts and rivets to make things a little easier. Thanks for everyones help!