Make sure that there is only a bit of pinky bellow left in the middle of the roast, none of this tv reality chef style cooking where the whole lot would be raw except for the outside layer that would be charred.
The brown sugar is important to the taste of the glaze Arctos. I can tell you it won't taste the same. If you use it as a brush on glaze you will only use less than half of the mixture. That mixture will cover a big roast. or two.