Is my WRR highway-worthy with this set up?

I've made some mods to my 2015 WRR to make it more dirt oriented. I'm a relative noob when it comes to riding dirt (although I'm totally loving it), so I wanted to get all the help I could from my bike set up. That said, I'd still like to be able to safely ride at highway speeds for a couple of hours when necessary. Not looking for comfortable all day slab touring on this thing, of course. And no need to go passing everyone in sight. Just something that will safely keep me at 65-70 mph for a few hours when necessary.

For what it's worth, unfortunately the offroad terrain I'm learning in really varies. Sometimes its loose sand and mud in the Jersey pine barrens, sometimes it's harder and rockier in PA, and sometimes just plain 'ol dirt roads.

Here is my current set up:

Tires
Front: Pirelli MT21 80/90-21
Rear: Metzler MC360 Mid Hard 110/100 - 18
I use heavy duty tubes (I think they might even be "extra heavy duty") and rim locks on both rims. The tubes scared me a little because of the "no highway" warnings on them, but the guys at the shop I go to tell me not to worry about it. Some googling kind of confirms this, but still curious about it . . . .

Sprockets:
Front: 13 tooth stock
Rear: 47 tooth

Chain: Renthal R3, 112 links. Box says "designed for off-road, enduro, and desert applications" and somewhere the instructions say "not for highway".

Should I be concerned about the WRR for brief (2 hour or so) highway rides set up this way?

Well this is a bit subjective and a lot has to do with what makes you comfortable.

For myself I run something pretty similar - 13/48, Pirelli MT16 front, and currently an AC10 rear. What I can tell you is those pavement miles will really eat up your knobbies so expect to change them about every 1000 to 2000 miles depending on how aggressive you ride. Probably the key thing to do is make sure your air pressure is up when you are covering distance on the highway. Follow the tire recommendations but typically I am usually up around 30psi if I will be on pavement for a bit. Once I get to the trails I drop the tire pressure down to 16 to 20psi depending on the surface.

One other thing I have found out is the front tire is more important to me than the rear tire. So I will generally give up some aggressiveness on the rear tire to get something that will last longer. D606 is a choice of many for the rear tire. For my front tire I typically only run a Pirelli MT16 or a XCMS since they don't seem to push when you get into the soft stuff.