Having relied mainly on the recently modified three-pickup Les Paul Deluxe as backup in April, Ace showed up in early May, 1975, with a Gibson Les Paul Jr. Gibson produced this version of the Jr, with a Les Paul-style single-cutaway body, from 1954 to 1958 but based on the knobs the one Ace played was most likely from the 1956-1958 range. (That said, as noted below there were some minor changes made to this guitar and it's not unreasonable that the knobs may have been changed.) It first shows up on May 3 and for about two weeks or so Ace seems to have been fond of it as there are several photos of him actually playing it on stage. The last such photo is from the show at Cobo Hall on May 16, 1975.
Ace retained the original dog-ear P90 pickup but there were a few minor modifications made. The tuning pegs were changed to Schaller M6 and the bridge was replaced. There are precious few photos that show the replacement bridge with any real detail and as of yet I have been unable to identify what it was. An educated guess would be a Leo Quan Badass bridge which seems to have been a favorite during this period. (But the photos available don't show the characteristic adjustment screws of the Leo Quan.) During the second half of May there are a few scattered photos of the Les Paul Jr standing side-by-side with Paul's backup Gibson Midnight Special on Ace's side of the stage but it doesn't appear to make it into Ace's hands after Detroit. It is last seen in Long Beach, California (below). There is, however, a void in June 1975 where there are no photos that show any kind of backup guitar for Ace.
In the 1977 Music Life Special there is a photo showing parts of Ace's guitar collection. In the front stands a 1955 Gibson Les Paul Jr but it doesn't appear to be this one. Even though the "Music Life Jr" has had the original wraparound bridge replaced, it still has the original tuning pegs.
Once we get to 1974 the number of photos—and, more importantly, the number of detailed photos—increase exponentially and we can begin to actually look more closely at the LoBue Custom.