I'm probably throwing myself under the bus here, but I've been through Gettysburg twice with a 53' and don't recall seeing any length restriction signs(however it was dark and raining both times). Not to mention I saw a number of others trucks doing the same thing. There are a couple of round-a-bouts but there is plenty of room to clear the curbs.
If the restriction does exist, I'll consider myself lucky and avoid the area until I get a clarification.