Sumerian cuneiform script was first deciphered in 1830s, so if Ichabod can read it, he must have learned to do so after his 'rebirth'.
The episode is directed by Peter Weller aka the original RoboCop.
At 10:06 "The Legend of Sleepy Hollow" is spoken for the first time in the series. It is, of course, the title of the work upon which the series is based. The short story by Washington Irving was first published in 1840.
At 32:15 the episode provides an alternate origin story for the expression "Don't fire until you see the whites of their eyes".