At 14 minutes, Luffy and Koby have to stumble away from each other to avoid a swing from Alvila. In one shot Luffy is still holding the oar in his hands but when the camera switches to Koby, it shows Koby removing the oar from his shoulders.
Around 10:21, you can see Zoro's Wado Ichimonji sword got bent.
At 0:01:14 -the structure is composed of 21st century steel forms which are welded together using a 21st century welding technique.