Quick script to use `/usr/share/dict/words` and count the amount words which can be inner-transposed to another word. Also prints the average length of words with alternates.

words_inner_trans_counter.py

from collections import Counter

words = []

with open("/usr/share/dict/words","r") as f:
    for line in f:
        words.append(line.strip())

words_list = []      
  
for w in words:
    if len(w) > 3:
        w = w.lower()
        l = list(w[1:-1])
        l.sort()
        l = tuple(l)
        words_list.append( (w[0], l, w[-1]) )
        
c = Counter(words_list)        

s_vals = [ (k,v) for k,v in c.items() ] 


s_vals = sorted(s_vals, key=operator.itemgetter(1), reverse=True )

#All the words with transposable alternates (inner anagrams?)
print s_vals

print "AVERAGE LENGTH", float(sum([ len(x[0][1]) + 2 for x in s_vals]))/len(s_vals)