Bob is pretty awesome at helping builders do custom stuff so he’d almost certainly help design the mount. Building it wouldn’t be hard.
You could get him an accurate FWF weight by removing the mount bolts in your current plane and hoisting the engine just enough to lift it off the mount. With this info Bob could determine if the engine needs to be moved aft.
Maybe noteworthy: I looked at installing a 550 and a 520 on my 4-place. I called a commercial operator I trust and asked his option. The gist was if your going to run the engine in their normal power range, which means 12-16gph for a 550 or 520, then either engine is great but the 550 is awesome. If your going to spend a lot of time loafing around at low power then both engines would be quite unhappy.