"Wonder is that young Dedalus the moving spirit. Has a good pair of boots on him today. Last time I saw him he had his heels on view. Been walking in muck somewhere. Careless chap. What was he doing in Irishtown?" Eolus
...the answer to this question of what-Stephen-was-doing-in-Irishtown can only be answered by resolving the devilishly complex side-issue of how the mourners were seated in the carriage in 'Hades'?
...other important mysteries can only be resolved when we guess what Stephen was doing in Irishtown?
A key piece of evidence, suggesting Bloom is at 1:00 or 5:00:
"a tramway standard by Mr Bloom's window" (p88)
...may appear as a dot between the 'B' and the 'R' on this 1907-1911 map but not on this 1906-1909 one. (Could the standard be on Westland Row? How did pointsmen route the trams? electrically or mechanically?)
Another suggesting MC is at 5:00 or 1:00 and SiD at 11:00 or 7:00:
"-- How do you do? Martin Cunningham said, raising his palm to his brow in salute.
-- He doesn't see us, Mr Power said. Yes, he does. How do you do?
-- Who? Mr Dedalus asked.
-- Blazes Boylan, Mr Power said. There he is airing his quiff.
Just that moment I was thinking.
Mr Dedalus bent across to salute. From the door of the Red Bank the white disc of a straw hat flashed reply: passed."
If the Red Bank is really to their right, it seems unlikely Boylan could see greetings from the 7 and 11 seats unless their occupants bent across. But there's a preponderance of evidence that Bloom is facing MC, so we'd have MC and JP at 5 and 7 (with JP's leaning across unmentioned), LB at 1, SiD at 11.
(I'm starting to suspect that Joyce meticulously constructed this riddle to emerge very very slowly from the vague language hints, like an old photograph developing.)