[JFP in PA]

Using thread chasers, not taps, clean out all of the bolt holes on the rear of the engine cases. Make sure you have the clutch fork in correctly, as well as the throw out bearing. I personally like to use two long bolts with the heads cut off in the 10AM and 2PM bolt holes to help line up and support the trans while reinstalling it. With the trans in the "ready to go in" position, slide under the back of the engine and make sure the mating faces on the engine and trans are parallel to each other (this is where most people go wrong), and then slide the trans onto the long bolts I mentioned while also rotating the axle hubs back and forth to align the input shaft splines with those of the clutch disc, and don't be afraid to shake the trans a little bit as you move it inward.

Putting one of these back in is a lot like threading a needle on a larger scale; you will fuss and fuss and fuss with it for what seems like forever, and it will suddenly go "clunk" and slide right in.