You'll need one of those nice shiny adapters to hang a 203/205 behind a 4l60, ..
http://67-72chevytrucks.com/vboard/s....php?p=3697343
Unless like what Russ said and you have a divorced tc
Or find a 700r4 4wd trans....you can also use a t350/400 as well...need to factor in tire size and axle ratios