Hobart Brothers sells an E7016 electrode, but only in a 50lb can. Call their customer service phone # if you want to order.
I've welded with a little bit of it. It is sometimes used overseas for an uphill low-hy root pass for high strength pipe. It's got more penetration than E7018, but less than E6010. Runs not as smooth as E7018.
If you have the open root bead with 7018, 7016 should be a snap
What you want are Kobe Rods. They come in 10 pound cans.
I may be sending you on a fools errand, but you can get them from Airgas. They can get them and you may find someone on the internet. Call Airgas in Hobbs NM or Odessa TX
One of the best welding supply houses in the oilfield is A & F Welding Supply2311 West 42nd Street, Odessa, TX 79764-6308 Telephone (432) 550-9353. As opposed to others it is ran by guys that know and support welders. They should have them or can get them to you quickly.
I have tested a lot of welders on the open root LH. With one exception, all who passed used the Kobe rods.
You want the land the same size or a little wider than the electrode you are using.
The same for the gap. If the opening scares you, you are about right. Remember, if the gap is a little wide, you can turn down the heat and slow down, but if it is too tight you will never get it in.
Coming off the tacks, keep the rod at 90 degrees to the bevel. It is almost a drag technique, but not quite. You may need to point the rod tip back toward the weld pool.
The heat setting is critical. And every machine is different. But there is a spot, and it is really small, where the rod just pours into the bevel and ties in.
As you come up on the tack, slow down a little as you come over the tack then point the rod toward the tack as you come off it.