I remember back in 1994 I mated a 4l80e to a 205.I did this without even realizing that GM did it(like dyeager said) in 91. The 205 was from a 85 with a turbo 400. If I remember correctly I had to take about 1/2 inch off the 4l80e shaft and some slight machine work to the oring groove was done to the adapter so that the large o ring between trans and adapter could fit right. I remember calling Advance at the time and they didnt know much but I remember being concerned about cutting the shaft down and losing some spline engagement but whatever(I cant remember anymore) the remainigr length after the cut was was plenty for strength according to them. I had it in a a 85 0ne ton dually cab in chasis and It worked great.