I feel foolish even asking, but I want to be absolutely sure about this. The kit I want to order has 2 orifices, one for LP and one for butane. I just bought a stacked kenmore washer and dryer that has been converted for LP, and I am going to convert it back to NG, but want to make sure that I am using the proper orifice, or if I need to order a different one.

You need to order the natural gas orifice.