Might not be of any help but reminds me of a story back in the 80's. i had to do an engine swap on a Bedford truck with a rod through the block, stuck in southern India.
I had just finished a trip from London and was in Kathmandu Nepal, anyway i had to fly to Bombay to collect the engine and get it down south to where the truck was stranded. this was another story on it's own.
Back to the Carnet question : The engine came into the country on it's own Carnet.
After a few days in 40 plus degree Indian summer i had the engine installed......casualties = 3 lost fingers and a crushed hand that belonged to one of my local Indian helpers, when this happened all my other helpers ran away!! at least i now had the cab back on. Eventually got on the road as i had to relocate the truck and trailer back to Nepal.
As the replacement engine was on a Carnet i had to load the old engine and take it out of India. I remember at the India Nepal border they did inspect both engines and stamped both the truck/trailer/old engine and new engine out of the country. Entering Nepal the Truck/trailer and old engine was stamped in and then they also stamped the new engine carnet into the country.
I am not sure what happened to the old engine but i believe it was custom cleared in Nepal and a new carnet was issued for the truck with the new engine, this was all done back in London.
By this time i flown back to London and was already on the road heading back to Nepal....this time via the USSR..........What a great time that was.
Kevin