There's a better picture of the circular plaque on p60 of the "Phaidon Architecture Guide to Dublin" (by John Graby and Deirdre O'Connor, 1993), which dates No. 64 "c1810". Julie Craig's "See Dublin on Foot: An Architectural Walking Guide" (Dublin Civic Trust, 2001) says on p16 that one of the plaques depicts Michelangelo's 'Moses'. (It also says that Johnston (1761-1829) rented the house to Isaac Butt (1813-1879), founder of the Irish Home Rule Party - which seems improbable.)
Vivien Igoe's "Dublin Burial Grounds & Graveyards" (Wolfhound Press, 2001), describing Johnston's tomb in St George's Cemetery (Whitworth Road, Drumcondra) on pp237-8, mentions 64 Eccles Street, "where he kept a number of bells in the stable to the rear of his house. These were rung on special occasions. Understandably it did not make him too popular with his neighbours. He presented these to St George's Church [in Hardwicke Place, his masterpiece, built between 1802 and 1813] in 1828. He endowed the bells with an annual sum, which was given to the ringers to hold a dinner, the condition being that the bells were to be rung on certain occasions, one of which was his birthday! Sadly too, they tolled on his death. The bells of St George's are immortalised in Ulysses: 'A creak and a dark whirr in the air high up. The bells of St George's church. They tolled the hour: loud dark iron.' With the closure of St George's Church, and its conversion into a theatre, the bells were transferred to Christ Church in Taney [Dundrum] and rang in the new millennium."