I don't know why folks think that they have to have matching front & rear track widths. For years GM SRW trucks have been narrower in the rear, and the Willys pick-ups were radically narrower in front (Wide-track Jeep/Scout II in front, full size pick-up in rear). Both drive just fine.
From a handling/performance point of view the ideal set up is slightly wider in the front than the rear. I'm fairly certain that this is why the GM trucks were set up this way.
What are the benefits? Better tracking when in a dynamic situation (i.e. accident avoidance or a slalom type of maneuver). To get a feel for this, think about a kid's tricycle. Quite unstable at any appeciable speed. Reverse it so that the two wheels are in the front and a single trailing wheel. Stable.
Also, narrower in the rear will give a tighter turning radius, very useful on a 4x4 obviously.
By slightly wider we are talking a difference of an inch to four inches typically. It's mostly restrained by packaging and realities of loading, geometry, etc.
To the OP, I'd use new wheels. If you decide to go with spacers get some from a reputable company like Spidertrax.com.