One swapper uses the 1MZ-FE. Many different engines will fit, I have even considered the 2.4 from the TC since there is strong aftermarket and the engine is very light weight compared to the 3s. I am kind of interested in the new 27xhp v6 they put in the Venza and its 6speed but its only an automatic for now and I am sure it is not cheap.
Info on a v6 into a fwd. http://celicatech.com/forums/showthread.php?t=13112
Info on a v6 into a gtfour. http://celicatech.com/forums/showthread.php?t=20037
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