Packing in an Amtrak style box in my mind is a superior solution but there are other solutions that will work. Getting a box to fit a 60cm vintage bike at your LBS is not a given. The LBS I visited in Portland is without a doubt one of the 10 premier shops in the country and the biggest box they had on hand was marginal. To make my bike fit will require spinning the front forks 180 degrees(pulling the front caliper and fender) and I still haven't verified that seat tube won't be too tall (I have to pull the front fender to verify). I could plan on pulling the back wheel as well but then I would need to pull my duopar derailleur which means removing the chain and hoping I don't lose any of the irreplaceable bits.
I used to be a decent enough amateur mechanic. In 1975 I converted my crankset to a triple and built my own wheels. On a Friday afternoon in October of 1980 in Krakow I pulled my pedals, wheels, and handlebars in less than 5 minutes and had my bicycle passed to me through a train window by a couple of drunk college graduate students. This was after drinking Slivovitz all afternoon. I didn't have a plan to ride over the Tatras and I thought better of it and bought a ticket on the train. But just as I was getting on the train I tried to check my bike as luggage they told me I didn't have the necessary customs forms and the customs office was closed for the weekend and I would need to leave the bike in their warehouse and they would take care of it for me and send it on to Budapest on Monday. But I needed to get on the train because my visa was expiring in 2 days. I am slower now but still capable of disassembling and reassembling a bicycle.
I think I am back to the Amtrak box and if I get stopped I check-in I will figure it out.