Hi Larry you raise 100% legitimate points. But I suspect a similar question was originally raised of Messianic Jews. The first step was to try and divorce biblical Judaism of the Torah from later Judaism of the Talmud. Then Messianic Jews could distinguish what was is really a religious issue and what is a cultural one.

The same with Islam. Many things we associate with "Islamic" are actually manifestations of Arabian culture, or the later Haddith, and not the religion of the Qu'ran. So a Messianic-Muslim shouldn't, for example, feel obliged to where a Burkha. 

And funny you mentioned head dress. The only religion with explicit commands about wearing head dresses is Christianity, in 1 Cor 11. Yet we explain those texts away today don't we? 

Muhammed was a deeply flawed person - but any more than OT prophets? His fundamental message was for Arabians to abandon paganism and worship the God of Abraham. Judge him by his time and place, not ours.