There are different opinions about the weight of the largest welcome gold nugget, i searched the info and found that the largest gold nugget ever found has the weight of of 2316 troy ounces or 72.04 kg and that was also known as the "Welcome Stranger".
if we divide that in three parts = 72.04kg / 3
=24.013 kg of weight each part
Now 1 kg = 32.1507 troy ounces
So, 24.03 kg = 772.036 troy ounces each brick weighs.