I am just not sure if this type of modding/usage is a common thing or not. If it was I wanted to take advantage of reusing my existing gear. Always learning
. I appreciate the insight.
It's not that common (any more), but it can be done. Here's how.
First, take your wing and either A) move it to the inside of your plate or B) run the waist belt through the bungee to help prevent tacoing. The first method works better with wide doubles wings, but with a narrow singles wing it will squeeze you like a jacket BC when inflated. the second method works better for a narrow wing, while a wide wing will still taco quite a bit. A third method (if you need or can take the extra weight) is to sandwich your wing between 2 plates (i.e. bolt a second plate on the outside of the wing where the tanks would be in backmount). This also works best with a doubles wing, but takes away the squeeze problem.
Second add a DR butt plate and/or drop D rings as far back on the harness as possible, and/or rings bolted to the bottom corners of your backplate and/or butterfly D rings on the back of the crotch strap (someplace to clip the bottoms of the tanks).
Finally, add bungees to your backplate. I recommend DR ring bungees (for all SM applications, really) but it is possible to make the other styles of bungee work, too (you'll just lose the ability to support the tanks out of the water, and to clip the bungee down out of the way when using your backplate for back mount).
That said, this setup will work for sidemounting, but it will not be as comfortable or flexible as a real purpose built SM harness. If you just want to try SM without investing a lot in a whole new rig, this can make a nice interim step for just the cost of some bungee, rings, clips, and maybe a butt plate.
I did this for a while when I was building my own setups, back before there were as many off the shelf SM rigs as we have today. I evolved from this to several iterations of DIY "razor-style" harnesses using some of the same HW methodologies before finally demoing Hollis, DR, and some other purpose built SM rigs and buying my X-Deep system. I still use the BP/wing system with the SM add-ons for side mounting my bottom stages and deco bottles with backmount doubles (for trimix dives, mostly), so it has not gone to waste.