Max,
You likely may have already had access to the "Ortsfamilienbuch Gross und Klein Elbe 1709 - 1875 mit Hofe und Hauserbuch." But, if not, I have a copy of it and it has 18 listings for BURGDORF/BURGDORFF families with at least 3 Johann Heinrich JULIUS BURGDORFs listed from Gross Elbe.
If you don't already have that information, let me know and I will pass it along.
Steve Bruer