Two words are dual if for every position where one word has a vowel, the other has a consonant and vice versa. Eckler's near-alternating ten-letter words in the August 2000 WOrd Ways exhibit many examples: themselves-Euroaquilo, literature-anatomical, clubfooted-audiophile, etc.
Constius, Hugo Brandt
"Lets Trade Phantom Monkeys,"
Word Ways: Vol. 34
, Article 25.
Available at: http://digitalcommons.butler.edu/wordways/vol34/iss2/25