A really nice posting, Scott! May you find what you're searching for!!!
I could take a look into the yellow pages of Frankfurt but I bet I would find many, many Langho(l)f(f)s...

Most names were built by any special circumstances which were related to their lifes. For example Mr. Smith is a name which were related to his profession. Another example is Mrs. Blackfoot who became her name by the circumstance that she had no money for buying shoes and so she had always dirty feet.
In your case the family name could be resulted by 'Langhelf' (engl.: Longhelp) or by 'Langhof' (engl.: Longcourtyard). In both cases there could be a big mass of people which are wearing this family name. And they must not automatically be related to each other...

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Greetings from Frankfurt (Germany),
Sheriff ;-)