You might want to swap the governor from the s-10 tranny (assuming it's a 4L60 [NOT to be confused with 4L60E!]) to the '85 tranny if you do the transplant, the flyweights are different between the two and the S-10 allows for higher shift points if balanced properly with the t/v cable adjustment.
As for the straight-axle swap, hope you have a good welder!
Ian