Like you I am researching HAVILANDs in the Glos area. Have seen several graves, and some folk have been very generous in sharing their research. At present I have about 15 relevant names plus lots of strays.
Let me know if you're still following this up. I see that you've heard from Kathryn, so it may well be that I can't add anything, but did you know that there's now a HAVILAND group on the GOONS, hosted by a lady who's been on the trail for 25 years.
Good luck
Colin