ATK remanufactured engines are good and you can get them from Quadratech.com. You can also get a good rebuild kit from ebay and have a machine shop put it together for you. When I had my 87 4.2 rebuilt, I had a few goodies installed. I installed a holley 470 4 barrel, offy intake, comp cam, rollor rockers, ported head, hipo pistons, header, ported head, HEI and MSD. It will run circles a round a 4.0, it screams with well over 200 hp. A lot of people swap in a 4.0 in place of thier 4.2. With a few old school parts, it will produce more power than a 4.0 and there's no computer or sensors to mess with. The 4.0 is an awesome engine, but I wouldn't trade 1 well built 258 for 2 4.0's and the lowend torque of the 258 is off the hook. It reaches peak torque at 1,800 rpm's, awesome for crawling a round off road.
1987 wrangler, 258 I-6, 5-speed.
2007 liberty sport 4X4, automatic
2009 ford ranger 4x4 FX4 OFF/ROAD, 5-speed