I will be honest with you, I'm not exactly sure about the "GRASS" method you are talking about, but I'll try to explain it as best as I can.

Since you are going from light years to light seconds, you will divide by 365 to obtain the length in km of one light-day, by 24 to obtain the length in km of one light-hour, and by 3600 to obtain the length in km of one light-second.

Therefore, 9.46*10^12/365/24/3600 = 3.00*10^5 km per light-second.

Hope it helps!