Are you planning on keeping the vehicle for your use or are you trying to flip it to make a little coin? If you are looking at flipping it I would pass on it. If you verified that both were running recently and not just the opinion of the owners then maybe I would be inclined to take chance. Does the owner of the engine with the timing guides updated have any receipt for it such as the parts he/she used or receipt from shop that did the work? Did the engine receive any cooling system updates at the time of timing guides updates? If you are not sure you'll spend another $1K-$1.2K on this with quality parts. Same for the tranny rebuild. Who did the rebuild and what documentation is their to substantiate the quality of the rebuild? There are a lot of ifs and unknowns here. Like I said if you were doing this all on your own and its a keeper then this move would make more sense. In addition is the condition of the vehicle you are trying to make whole in excellent shape and what kind of miles are on this unit? All this needs to be evaluated to make a better decision to proceed? In addition you need to keep in mind that you are going to probably spend more than the initial outlay of $2600. You will want to do a system cooling service/refresh on the 4.4L, valley pan gasket is a common wear/failure point. If the 4.4L engine is high mileage I would also do a rear main seal replacement. Before you know it your $2600 outlay has escalated to $4k outlay. Once again if you are keeping this for yourself then may be more attractive as a hobby/project build but if your looking to make a profit on a flip, risky.