Look for split vacuum lines, usually coming from the evap system above the gas tank in the rear.
That's where I found the cracked vacuum line on my wife's '03 KJ which gave us the same code. It was an easy fix! You can reset the light on your dash by disconnecting the battery for ~20 minutes, but if your state plugs in to scan OBII vehicles, that won't solve your issue - the truck will still fail because the monitors need to be reset. My recommendation - replace the cracked rubber hoses, disconnect the battery for ~20 minutes or so, then reconnect. You'll need to drive it for several drive cycles (usually a few days) before all OBDII monitors have been reset and the code doesn't come back, then get it smogged.
Oh, as far as your wheel situation goes, here's what I've found. 16" ZJ or XJ wheels will fit fine especially with stock-size tires. Some factory 15" ZJ or XJ wheels ~may~ work - I remember seeing a KJ around here with 15" Ecco wheels, but it was on the road so I don't know how much clearance there was by the caliper. Personally, I think the aluminum 15" wheels have a better chance at fitting since they don't have the hump behind the spokes like a steel wheel. I tried a 15" steel wheel from an XJ on my wife's KJ and there was hardly any clearance between the inside of the rim and the caliper - see the pic below.
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Also, 16" TJ wheels will fit (like the Moab wheels). The WJ, WK ('99-up Grand Cherokee), and JK ('07-up Wrangler) wheels will not fit, since they are a 5x5" bolt pattern - the KJ, XJ, ZJ, TJ, and even YJ are all 5x4.5". Hope that helps ya!