First they are different engines. The 99 has a pushrod 4.0 while the 01 uses overhead cams. If you want to get the SOHC engine I would look at a 04 or newer engine since the 01-03 engines have timing chain tensionor problems. I would say that the engines use the same mounts but I'm not sure about that.
Also the you would have use the correct tranny for the SOHC engine.