try manxnotebook (tabline above) - look under towns; follow churches link off that page to find details about the two excellent books by the Radcliffes (tho I think now out of print but try the shop at manx Museum enquiries@mnh.gov.im to confirm this)

There are a couple of books on Manx postoffice - Mail of Mann is one (I'm not 100% certain of the title and can't find my copy)