It would be easier just to build your 4.2. With a few old school parts my 4.2 makes well over 200 hp and there's no computer or sensors to mess with, plus you retain your manual fuel pump. People are to fast to throw the baby out with the bath water. The 4.0 is an awesome engine as I've had a few, but so is the 4.2 witch makes peak torque at 1,800 rpm's. If I had a 4.0, I would keep it, just as I would keep the 4.2. For the cost of the swap, you could of added a 4 barrel, intake, cam, header and so on, or you could inject the 4.2 if carbs aren't your thing. On mine I had installed a holley 470 4 barrel, offy intake, comp cam, rollor rockers, ported head, header, hipo pistons, HEI and MSD, it screams. I can't knock anyone for wanting more hp, but there are easier ways to get it without swapping and adding a computer, wires, sensors, electric fuel pump and so on. Just my 2 cents, 4.0's are great, good luck with your swap.
1987 wrangler, 258 I-6, 5-speed.
2007 liberty sport 4X4, automatic
2009 ford ranger 4x4 FX4 OFF/ROAD, 5-speed