Spoonerisms by definition swap sounds, but when written they are often ANAGRAMS that also swap letters, like Spooner's alleged "a wining shit" for "a shining wit". EYE SPOONERIMS are word pairs that swap letters and look like Anagram Spooners but don't swap sounds.
Word Ways: Vol. 45
, Article 20.
Available at: http://digitalcommons.butler.edu/wordways/vol45/iss4/20