If the rolling trick Steelheadz suggested doesn't do it jack up one front wheel (have the rear blocked for safety). Watch the tire as it comes off the ground. If your driveline is torqued up it will turn as you get it off the ground. Now you should be able to get it out of 4L. Check your tire sizes and pressures (to be sure you have all the same size tires). Since you just got the Jeep check the axle ratios (should be the same) in case someone swapped one out. The old transfer cases sometimes get stuck in low but generally you can get them out like Steelheadz said or, worse case, by backing up about 20 feet in a straight line, stopping, then shifting out. Best of luck - John
The driving backward 20 feet or so, then throwing transmission in neutral and then shifting the t-case has always worked for me. The original owners manuals that came with the old CJ's suggest this method.
Oh yeah, I'm glad you got your t-case out of 4lo. It seems like every old jeep has their own trick to get it in and out of gear. My CJ goes into 4lo kind of tough, but it comes right out.