Reading various forums for 15+ years, I think I know pretty much all of the pain most people go through reassembling or building their Mustangs. Each of us typically can relate to each of these, as we've pretty much experienced them ourselves. Sometimes, though, you scratch your head why folks have such hard times when it was easy for you.
Here's my example...
When Midlife was reassembled, I had to mount both doors by myself. Now everyone says alignment of doors can be time consuming to get them perfect. I did both of my doors within 1 hour total, first time mounting. I applied painter's tape to the door flanges (just in case), and got some paint stir sticks out. My car was on my lift, and I could set it to any height I wanted. I knew I needed an assist of some sort to keep the door at the right height, so I eyed a wooden picnic bench I had consisting of two large planks with a slight gap between them. I put the lower pinch weld of the door in this gap, raised the car on the lift to match the height of the door hinges, and maneuvered the bench/door combination up to the A-pillar. I started all of the bolts, raised the car to remove the bench, and proceeded to tweak the alignment, using the paint stir sticks as my gap manager between the bottom flange and the rocker panel and the rear flange and the B-pillar.
Slick, easy, and done in less than 30 minutes a side.