If it is silver in color, and looks the same (exhaust exits the END, not down or to the side) it is probably Ultra-Thrust (nelson) muffler. That will work great... bolt it to the hyper 50 and give it a try. You might want to try a 9x8 prop along with the 10x6 at first - get a baseline rpm to see where you are. You want to target somewhere between 16,000 and 17,500 rpm with your prop selection.

If the muffler exits side/down and/or has a long bolt running through it for assembly, then it is not a true tuned muffler (one of the Tower .46 type mufflers - inadvertently semi-tuned).