It not that its hard, but you have to know what your doing. Should drop right in BUT, there are a few minor set backs. Are both truck standard t-mission or autos, or is one an auto and other a standard? Finding what tranny your using is going to be the problem unless you take the entire drive train from the rolled truck and toss it in the 89. then drive shafts wont bolt up, u'll have to change, blah blah blah. If you have the time and some what coin in your pocket go for it. It shall be a learning experience. How hard was it to put the 4.0 in your truck, if you even did it yourself?