Diablo – still get level 60 hellfire ring if I have a level 70 character

Yes, you can do it.

Let your friend create a game with a level 60 character, join with your level 70(and maybe let your friend(s) join with their level 70 characters) and just kill all the ubers.

Just don't forget these 2 things:

• Even at Torment 6, you will only have 50% chance of getting an organ
• You can only craft a level 60(iLvl 63) Hellfire Ring, which is not even half as good as a decent rare level 70 ring

And as you said, getting a level 60 ring with a level 70 character should not be tough at all(especially when you compare dps/toughness people had at level 60 and now, at level 70)

Character level does not influence the level of dropped plans, it might influence what plans drop, but a plan for archon spaulders of strength is always going to be a level 60 item. This goes for all dropped recipes. If the resulting item is a Legendary, a set (basically a subclass from legendaries) or a rare doesn't matter.

The crafted items will also always be crafted at the same level regardless of what level the character crafting them is. A lvl 1 character can craft lvl 70 items.