Finally completed this puzzle, not without a struggle (17 took an especially long time) and am completely bowled over by its brilliance. Whoever Twin is, he - or she - must have a brain the size of a planet. What a superb way to entertain us and exercise our minds.
r-passing
6a - wordplay is 2+3 all backwards; +2. Teamster's heart gives 2 letters, 3-letter word for 'eye' and usual 'when; at the end.
30d - the long word is superfluous. Wordplay is 4 letter 'transfer' with a 2 letter 'tree' inside.