I have no concerns about your baffle, it will be slightly helpful and will do no harm. However there shouldn't be anything hot enough to burn foam coming out of the muffler. It may have been backfiring at some point, during its sad days when it was cooking itself to death.
I had a vertical crankshaft Kirby Lauson long ago that chuffed back through its air filter while it was stopping, setting fire to the foam. I let the foam burn, and gave serious thought to letting the mower burn. It was by far the worst mower I've ever had. My point here is that burned foam is not necessarily caused by hot exhaust gases, especially on a Kirby Lauson.
