Easy to tell how much engine braking you will have. Accelerate very quickly, in a lower gear let off, and if your nose hits the windshield. You got some engine braking. If not, you don't.
It is true that in general diesels have little to no engine braking, Unless it has some sort of trany brake, or exhaust brake. I have brought big truck diesels down mountain grades, they pretty much freewheel. It's like coming down in neutral.
However, You can safely do it. Just come down really slow. Watch the road warning signs, and do as they say.
And don't fall for that******about there being no steep grades in the NC mountains. There are. You just have to pay attention, and be ready. IF you start to smell your brakes, STOP, and let them cool off. NEVER use Over drive in the mountains. Any part of it. A sure way to smoke brakes, even in the relatively flat parts.
Just take your time. You'l be fine