There was definitely some waiting to find parts, as I was seeking 11speed 105 NOS (the crank is 12speed, don’t tell anyone) but mostly I just wasn’t in a hurry. Riding other bikes in the meantime.
Challenges, honestly not many other than finding NOS Shimano parts. Rear hub went in without having to cold set; brakes bolted right on, and sticking with a quill stem the cockpit was easy. I guess getting the special tools to remove and install the headset was a little hiccup. I had never run brake and shift cables/housing, so there was a learning curve there.