I have a 3sgte that I'm intending to put in my ke70.
Toymods is a painfull place to try find straight answers on how to convert a 3s to rwd. Most people posting on there have never tried to do the conversion however they are more than willing to tell you that cirtain part fit and they don't. They have a detailed posting on joels celica which is good, however he fabricated a lot of parts himself. Thats fine if you trust your own welding or have to much cash. I think he used a cross member and engine mounts of the corona. You would have to check that.
From my experience the hardest part is the bell housing, clutch, flywheel and starter motor.
I have seen an old celica that still used the original intake of a gt4. Bonnet still closed.