I think the 85.5-86 SVOs are different as fair as the SVOs go.
If you click on this link and then on FAQ its got some realy cool info on most of the turbo 2.3T like what turbos came in what and which EEC etc. I think the only one different in is the 85.5 -86' SVO and the 85.5 -89 XR. I hope it helps you out some it did for me