If you bought the Alp with the bindings installed, try contacting the seller to see if he has the 4x4 discs and the cant insert, the race plates always came with both sets of discs, but didn't come with cants til later on. You could also demo the boards without the cant, try riding the Alp without it in place. And, as pointed out, anybody that sells burton will have the discs available-they are not specific to the race plates.
At your weight, I would not worry about the sturdiness of the Burton plates, either.