3" leveling kit
#1
#2
To make it a 2.5" you only need to take off a total of 1/8". The lift isn't linear. I think the 2" is 1 5/8" thick and the 2.5" is 1 3/4" thick. So you would need to take a 16th off each side. If yours is anything like the Autospring, it is basically 2 flanges with a spacer and supports welded in between so i'm not sure if you would want to mill those flanges down. If it is a solid spacer, i'd say do it.
#3
#4
I would say return them and buy something else. I bought the 2.5's from this site I found searching for deals: fatbobsgarage.com. the spacers are about 100 bucks which are just like all the rest but about 50-100 dollars cheaper. I would go with the 2" my truck sits a little higher in the front than back now... one day ill have the rcd 4.5/6 suspension lift.