OK, here we go.
I have a 4 bone Hereford Prime Rib Roast I am going to cut in half and have for Christmas and New Years day.
I called the meat dept at our local HEB and they told me a 7 bone roast could weigh in the 15 lb range.
I thought they were wrong until I pulled out my 4 bone......probably 6 lbs give or take.
So I really suggest not hanging. Use the Grate.
I grabbed my extra PBC grate and did some measuring for ya.
My 4 bone is about 8 inches wide and 9 inches deep. Height of the roast is a non factor in the PBC.
Setting my 4 bone all the way over to the right still gives you about another 8 inches to play with the added 3 bones of your roast.
I think you will be fine.
However, if the roast is still too big a bit you could always lay it on the grate and give it some smoke....the smoke won't know it is laying perfectly flat or not.
Take it out when the internal is about 100 and finish it in the oven. It will have gotten more than enough "grease fog" flavor and the oven will take it to the home stretch.
I would pull the roast out when you are about 3-4 degrees from your target temp cause it will continue to cook. Lightly tent it with foil and let it rest a bit 10-15 minutes. The juices need to distribute back into the roast so they don't end up all over your cutting board.
I suggest keep your rub simple. 50/50 coarse kosher salt and ground black peppercorn will do the trick. You could add some garlic powder if you wish.
Here are the pictures........who says The Smoke don't love ya