Great question. I didn't have plans to. For enemies, following the table of health and attack rating should do it. An enemy with 5 or 6 health and a 2 attack rating is going to be about an even match for a character with 2 or 3 skill die. I've seen 1 tough enemy with 10 health and 3 attack rating almost take out two characters with 3+ skill die.
Only advantage and disadvantage should change the check die. Everything else should change the skill die. Also, skill die should only succeed on a 6. Anything less and the balance will be thrown off.
Does that help?