I dont have any Thoms to the early 1920s... closest dates I have are 1914 and 1927, which I am comparing (along with the census and the '39 electoral register) at the moment to see if I can track the changes and new roads in the area by monitoring addresses and household names..
Quaxer checked Thoms 1923 and 1929 for you in an earlier post (see
Reply #1) and saw no mention of St. Clare's. Maybe with these possible Seafort/Beach Rd connections it might be worth another look if he spots this post ..
O'Briens Place was off Haddington Rd should be induced on my 1912 map, which is online, but the street is not labeled.... I think I described the location before in a post for someone, I'll have a search for it.
Shane