mmmm standard 4L60E's arent too good with the torque handling when stock....
rebuild your V6 box with strengthened clutches and bands then see how it goes
The V8 4l60E has a diiferent bellhousing to suit the V8 enging bolt pattern. where the v6 is narrower. the previous statment is right the input shaft is different. yet so is the convertor and case.