that backplate style mount isn't REQUIRED, it's just a pretty darned convenient way to mount the engine.

Leave the baffle in the muffler, it has to be there.

There really isn't much in the way of "modifications" that you can do. Changing gaskets is allowed, so folks often use different head shims to lower the head a bit. Check the rear bearing - if it has a plastic ball retainer in it, you're ok. If it's stamped steel, I would recommend changing the bearing for one that is plastic. With the 9/6 props, the steel ones have been known to come apart and ruin perfectly good engines.

Some folks back out the idle screw in the carb and secure it with a little loctite, only screwing it in far enough to stay put. Engine won't idle that way, but it will shut down when you want it to.

Some replace the long bolt through the muffler with either a larger bolt or a piece of 6-32 all-thread, etc. They've been known to break and you lose the back half of the muffler.

Most important - break it in well, practice a lot. That makes more difference than a few extra RPM. MUCH more difference.