Solomon Allen is my 2nd great grandfather as well. He was born about 1831. He is next to impossible to trace. I have been working on him for some time now. He married Emily Jane Ealy in 1853 and as far as we know, they only had one child, John Thomas my great grandfather. Pretty much my Allen line stops here. I have been unable to find any absolute proof of Solomon's parents.
I am happy to share my Allen info with you if you think it might help.