When you have to ship your carburetor one of the best ways is by the US Post Office. USPS has what is called priority flat rate boxes.
There are two sizes you can use. Medium and Large. The boxes are free and shipping is around $9 for the medium and $13 for the large. Most 1 and 2 barrels and some 4 barrels will fit in the medium box. You will probably have to remove the threaded rod that holds your air cleaner on.
Be sure to wrap your carburetor well with plastic so that the gas smell doesn’t come through. Alcohol will also help remove the gas smell.
Priority flat rate takes two to four days to arrive.
Medium box dimensions 11 x 8.5 x 5.5
Large box dimensions 12 x 12 x 5.5
I think this is one of the most painless ways to get your carburetor to the rebuilder.