Sounds like you're gonna be just fine!
The brisket flat is just that.....the flat. It's had the point removed and has likely been trimmed somewhat. A whole packer or whole brisket is usually untrimmed with the point attached to the flat.
It sounds like you don't plan to foil? Many don't, so if that's your intentions, you'll be fine. First brisket I did was a flat and it was recommended to me to foil once it hit a point where I was happy with the bark. I did that and added about a cup of beef broth into the foil. To date, that was the best brisket I've ever done.
Personally, I don't think the pork dripping on the brisket will really help, but it won't really hurt either. The drippings will just roll off of the flat. Some think that the drippings will keep the flat moist, but they won't penetrate the meat really. Still, it's like basting....can't really hurt.
Let us know how it goes! If you have a probe thermo, use that to tell you when you're getting close. With both the butt and the brisket, it's not about temp, but tenderness. You're right on the money to look for probe tenderness (BUTTAH!). I like to use a thermo to let me know when to start checking for that. Usually once you get to about 180-185, start stabbing those suckers every once in awhile until you achieve total tenderness.
LET US KNOW HOW IT WENT!!!
18.5", 22.5" OTS
Large BGE (chambersuac's)
The Fiery Furnace (chambersuac's)
Big JT's Smokin' BBQ Competition Team