The statue of Smith O'Brien on Sackville street (where it meets D'Olier street) was unveiled 1870, the first monument in Dublin to commemorate a revolutionary Irish nationalist. It is seen here with Carlisle bridge (O'Connell's monument is not up yet).
William Smith O'Brien (1803 - 1864) was born in Co. Clare, and was educated at Harrow and at Cambridge. He became M.P. for Ennis (1828), then Limerick (1835). Originally a conservative Protestant 'Country Gentleman', his views gradually shifted to the left. He worked for Catholic Emancipation, Irish poor relief, and state support of the Irish Catholic clergy. He joined the Repeal Association (1843), became a leading member of the Young Irelanders, and a founding member of the Irish Confederation (1847). He was active in relief from the famine. In 1848, he urged the formation of a National Guard and an armed rising. The revolt was abortive, the only engagement being a skirmish with a police detachment in Co. Tipperary. O'Brien was arrested and condemned to death. The sentence was commuted to transportation to Tasmania. He later was pardoned, returned to Europe and Ireland, no longer active in politics.
"Must be his deathday. For many happy returns." (U6.227)

The inscription on O'Brien's statue reads:
'Born 17th October 1803
Sentenced to death for high treason on the 9th October 1848
Died 16th June 1864'
so Bloom's speculation is valid.
"The carriage wheeling by Farrell's statue united noiselessly their unresisting knees." (U6.227)

The statue of Smith O'Bien was the work of artist Thomas Farrell, who also did Sir John Gray's statue further up the street. It was of Sicilian white marble, ten feet high, and paid for by public subscription. O'Brien is shown wearing an ordinary frock coat, with his arms folded, and his weight borne on one leg.
"Oot: a dullgarbed old man from the curbstone tendered his wares, his mouth opening: oot.
- Four bootlaces for a penny." (U6.229)
"Wonder why he was struck off the rolls. Had his office in Hume street. Same house as Molly's namesake, Tweedy, crown solicitor for Waterford." (U6.232)

[Note: this is not Martin Cunningham]
"Has that silk hat ever since. Relics of old decency. Mourning too. Terrible comedown, poor wretch!" (U6.234)
"Kicked about like snuff at a wake." (U16.235)
"O'Callaghan on his last legs." (U6.236)

[Image courtesy of the ZJJF]
"And madame. Twenty past eleven. Up. Mrs Fleming is in to clean. Doing her hair," (U6.237)
"humming: voglio e non vorrei. No: vorrei e non. Looking at the tips of her hairs to see if they are split. Mi trema un poco il." (U6.238)
"Beautiful on that tre her voice is: weeping tone. A thrush. A throstle. There is a word throstle that expresses that. His eyes passed lightly over Mr Power's goodlooking face. Greyish over the ears." (U6.239)
"Madame: smiling. I smiled back. A smile goes a long way. Only politeness perhaps. Nice fellow." (U6.243)
"Who knows is that true about the woman he keeps? Not pleasant for the wife. Yet they say, who was it told me, there is no carnal. You would imagine that would get played out pretty quick. Yes, it was Crofton met him one evening bringing her a pound of rumpsteak. What is this she was? Barmaid in Jury's. Or the Moira, was it?" (U16.244)
"They passed" (U6.249)
"under the hugecloaked Liberator's form." (U6.249)

The Liberator is Daniel O'Connell (1775 - 1847). Huge indeed, the bronze statue of O'Connell wrapped in his cloak is 12 feet high, and the overall monument 40 feet high. It is still a major Dublin landmark. The PC reads: "Unveiled 1882. Winged Figures represent Fidelity, Patriotism, Eloquence, and Courage."