Dave, what a pleasant surprise.
Capt LH Davey is my GGG Grandfather and William Wilkins, my GG Grandfather. Your research has been fairly accurate about the family, the voyage on the Amelia Thompson, and the house and estate, "Sarn Fawr". A small book has recently been published by a local Welsh resident: "Sarn Fawr, The History of Sarn's First House". Land deeds first refer to the property in 1707 and it seems the farm house was first constructed a year or two later. But it was Leyson Davy who carried out major building/extension to the house in 1820. I have a later picture and painting if you are interested, but I suspect that is becoming a bit too remote for a person mainly concerned with the stamp. I have also written quite a bit on Capt. Leyson Davy (he was quite a man) so I would be delighted if you could scan the letter and envelope (front & back) and email them to me at firstname.lastname@example.org
Dave, may I enquire who your grandparents were as their possession of the letter would indicate a distant relationship with William Wilkins and therefore with myself? I also have pictures of both LHD and WW.
Regards from Sydney Australia,