I'm not sure about the spelling. My great great grandfather was in the U.S. by 1850. He's in AR by 1880. I have land records that he signs Joseph Mrossowsky, but the "double s" is written like a "p" (the German buckel as you state). Our name was shortened later to Mross. That was my maiden name. I can't find anything on him previous to 1850. Census records show he was born in Poland.