Don't let it worry you too much...there are several SMB's out there with semi floating rears. Like most stuff, equipment is usually designed to exceed what we put to it. But once you start to change the stock items (like adding spacers) you begin to go outside what it was designed to do. If you tow, travel tough terrain on a regular basis, or constantly overload your vehicle, a light semi floating axle is subject to failure. Is it guaranteed to fail...no, but it's like a 300 lb guy sitting in a 250 lb rated chair. You never know when it will collapse.
More than likely, if SMB did the conversion and it has spacers, you have a semi floater. Here is a thread to help you:
viewtopic.php?f=39&t=8543