3.8/4.2 mods

hi i am going to rebuild my 91 3.8 soon and was told at one time that i can swap a 4.2 crank and rods to produce a 4.2 but the only 4.2's ve found are 97and up but my 3.8 is a 91 and im not shure if the 97 crank will fit in my 91 3.8.If any one knows any thing on this it would be apreceiated

peace

also would i have to change the computer or any thing els with this??