I have run up against an early brick wall. I have found what I believe to be all the initial possibilities for 4ac/18dn (4-digit powers) and likewise for 7dn (2-digit powers) , which lead me to only one match for the intersection of 4ac/7dn. But when I then turn to 18dn (the other 4-digit power) and add this to 7dn, so as to solve 6dn, I hit my brick wall.
I can only assume that some 2-digit or 4-digit powers are escaping me but I'm blowed if I can see what they are.