I've made several internal-frame packs with 70d ripstop. It's not nearly as durable as the heavier fabric, but OK if you take care of it. On an external frame pack, I wonder if the 70d wouldn't wear quickly where the bag contacts the frame crosspieces.

On the Kelty D4 frame, the grommeted flaps that fasten to the frame would need to be reinforced, either with extra layers of fabric or maybe some thin webbing.

Regular grommets will work...I've made several packbags for external frames and had no problem (with heavier fabric.) Spur grommets were used on the Kelty, and are better, but the setting tool is expensive.
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Always remember that you are absolutely unique, just like everybody else. -Margaret Mead