Your rear leafs will settle after time and a few hard wheeling trips. The nice thing about leafs springs is you can pull leafs out to keep it level. After a year or two you can add back the leafs you took out to keep it level after they have settled in. This allows you to keep up with our every chaning bronco's, hard top to soft top.
I would go with 5.5" leaves put it together run it for a few months, then pull what you need. Rear springs cost about the same, 3.5" or 5.5".
my $0.02.
Good luck.