When the 6 soldiers carry Lincoln in his plain wood coffin down the stairs and set it into the waiting wagon, the box is clearly empty as the 6 men show no strain in hand or shoulder as they lower the box into the wagon.
Andrew Johnson, while getting dressed, uses the modern phrase "get this show on the road." The phrase was not commonly used until the 1940s/1950s and would not have been used in 1860s conversation.
Use of the noun "creep" to refer to a detestable person is profoundly anachronistic as it did not come into use until the 1930s and '40s.
No one would have said, "Congrats" instead of "Congratulations" to President Johnson after Lincoln's assassination. The 19th century was known for its formality and verbosity, so such a colloquial abbreviation would never have been spoken in any context.
There was no standardization of shoe size until the early 20th century. Shoes at the time of Lincoln's assassination would have been custom-made or adjusted to feet each individual's foot.