I am descended from the John Maguire who arrived in South Africa. I have a sketchy pedigree chart of the Maguire family, but I would love to have a copy of the document you have, which is signed by Sir William Betham. I am also looking for information linking John Maguire to the rest of the family.
I went to the Dublin library some years ago, and made a copy of some of the pages of the book Brian Maguire wrote - he was certainly eccentric!
I would appreciate any information you can give me.