As a result, my answers can only be partial in nature:
(1) Did this get a theatrical release at the time?
My understanding is that ANGEL'S FLIGHT was filmed in 1963 with a production crew assembled from a variety of local independent film tech personnel under the overall guidance of William Thourlby, who'd been pitched the story idea by Dean Romano. It sat around for nearly two years before a deal was struck with Crown International Pictures, an LA-based company that mostly worked with independent production entities on projects that covered the gamut of the burgeoning exploitation market. Some scant evidence exists that it did have a brief theatrical release, but only in selected California venues.
(2) The print I watched on YouTube ends abruptly, followed by a repetition of the opening credits. I assume that is a problem with the existing material? The movie once ended more conventionally?
It's presumed that when Crown went out of business in the 80s, that the original elements were lost or discarded, so there's still some uncertainty about the actual ending of the film. The version on YouTube seems to stem from the copy in Dean Romano's possession, which was the one screened at the Egyptian in 2006 (and again in 2015).
(3) The IMDB offers this nugget: “Crown International's TV version was re titled SHOCK HILL, and featured new wrap-around segments featuring original cast member William Thourlby, in which his character looked back upon the events of the original ANGEL'S FLIGHT film.” Do we know any more about this? Year it happened?
Records indicate that Crown's TV version was created in 1968 and screened briefly at that time. It does not appear that this version has survived.
(4) Is there any likelihood of a restoration? Jim Dawson mentions the existence of a 35mm negative.
There was talk of a restoration in the years immediately after the 2006 screening, but there seems to have some type of rights dispute over the film that prevented that from happening.
I think these questions might be put to Eddie Muller as part of his "Ask Eddie" feature to see if either he or Alan Rode have kept more abreast of the film's status. William Thourlby passed away in 2013; the IMDB has not listed a death date for Dean Romano, who'd be in his mid-90s at this point if he is still with us. The current status of any negative for the film is unknown.
Dawson’s book on Bunker Hill discusses how the waning years of this neighborhood were self-consciously elegiac, and that is certainly true of this movie, with its discussions of how the Hill needs to be memorialized in print. The use of the locations along with the frequently fresh camera angles builds a convincingly realistic world on-screen.
I noticed that this is by far the most Bukowski-esque film I have ever seen, and in fact one can easily imagine Charles as an extra in the bar scenes; he was in his mid-40s at the time and haunting just such places.
The isolation and loneliness on display are of a piece with other early Sixties independent films such as Blast of Silence and Carnival of Souls. They all share a mood. Angel’s Flight pushes towards roughie territory without perhaps quite arriving there.
All of the above is (IMO) absolutely on-point. A restoration would certainly lift the film into a higher realm of estimation (and would vindicate the oddball career of cinematographer Glen Gano, whose biggest claim to fame is a series of Three Stooges shorts shot during WWII but whose career stretches back to the silent era). As Dawson notes, Bunker Hill had acquired a cult following in the early 60s as narratives of urban blight radiated across the USA--its prominent identity in the subculture of Hollywood gave it an added sense of romantic doom; the name of the funicular clearly augmented that as well.
ANGEL'S FLIGHT also benefits from the youthful beauty of Indus Arthur, a prototypical sixties waif whose look is a clear precursor of the hippie movement that would shortly explode onto movie screens. The faraway sadness in her gaze was a perfect fit for the tragic protagonist in ANGEL'S FLIGHT but was too subdued to register in the increasingly frenetic landscape of the later 60s; by the early 70s she had shifted her career toward music (singer and harp player) and became known as a performer of old folk songs at Renaissance fairs. Sadly, she battled skin cancer for nearly a decade and passed away at the too-young age of 43.