Can a 02 Saturn 2.2L ecotec engine be put in a 04 cavalier?

Yes, it should. The '01 2.2 liter OHV is the same one (with some minor updates over the years) as the one from '96 (think it was developed in '92-ish) it wasn't until '03 did Chevy change to the 2.2l DOHC Ecotec.