Awesome!!!! Your in luck.
Let the roast come to room temp. Have a meat thermometer. Since it's already seasoned and ready to go.
Preheat the grill. I keep mine between 250-300.. Depending on size and cuts of meat.
Load up the spit. Place a pan underneath it to catch the drippings and let it go. Until the temp reaches 140 degrees. Let it rest and carve..
Here's a chart for grilling. Your charts towards the bottom.
Beef Cooking Times: Easy How-To Cooking Tips & Advice: RecipeTips.com