Hi Chris,
All three of those men appear in Peter Hinchliffe's "The Lent Papers: Helmut Lent" (ISBN 1841451053):
- Kubisch was Lent's regular Funker from the beginning of the war until his last flight on 7 Oct 44. He was buried next to Lent on 12 Oct 44 in Stade, and posthumously promoted to Leutnant. On 31 Dec 42, Kubisch had become the second Funker to receive the Ritterkreuz. There are over two dozen passages in the book that mention him.
- Reinthal gets a couple mentions when he takes over as Lent's Funker after Kubisch is severely wounded on 8 Jul 41.
- It seems Lüttringhaus only flew with Lent on a couple of occasions, but one of them was very significant -- a mission on 16 Jun 44 in which Lent claimed his 98th, 99th, and 100th kills. There is a photo of Lüttringhaus on page 247.
FYI, there was a period during the first part of May 41 when Kubisch wasn't flying with Lent, for reasons that aren't clear. During that time, the following Funkers flew with Lent: Friedrich Johrden, Wengorsch, Hummel, and Zwickl.
Hope that helps,
Leon Venter