Spacers might work, but you'll have to consider a couple of things. One, is there room to move the wheel closer to the fender, and two, how big of a spacer will you need vs how long are your wheel studs? If you have outward room, spacers may be a cheaper option, but only if you don't have to buy 3" studs, pull the axles and have them pressed in.
I'm with everyone else so far on this, the best way to do this is to relocate the springs. Dr Diff's 1" relocation kit should be fine, and it shouldn't really change anything significant other than the location of the perches on the rearend.