You can go to the JAL Cargo site at http://www.cargo.jal.co.jp/FLT_DSPe.htm
, enter the flight details, and be able to check out the actual registration and aircraft type of any JAL flight for the next two days.
Based on the information from the past few days, those two JAL flights seems to be using 747-300's consistently. I doubt their 743's will have their most up-to-date Y-class cabin. In fact, my relatives who recently flew on some of their 743's commented that the seating is rather cramped.
Sorry for the "bad news"!!