Nothing in the USPO regs that states the firearm must be disassembled that I can see or am aware of.
I have been told by many clerks that it is so,,but when I ask them to show me where it says it must be disassembled, they never can find any.
It must be unloaded of course and it states that very plainly. They reserve the right to open and inspect to confirm or may demand written certification of same from you. That is in the regs.
43 Firearms
Not every firearm that is C&R is on the posted BATFE C&R list. Many of those are one-of firearms and modern collectables that have been added after application for C&R status from individuals.
The guide line of 50 yrs/old or older from todays date is one that is posted on the BATFE site and will cover the field in general back to Antique status firearms. You have to be able to prove the age of the firearm by published data or direct date stamping etc. No guessing on those close ones and watch out for State regs that vary the Antique status date. Some states don't even recognize C&R or Antique status at all and may treat either or both as transferable through an 01FFL only