As always you come up with some beautiful examples, and while I defer to the expertise of Dmitry and Glen on these U.S. swords, I just wanted to say it certainly looks like Peterson #108 to me. I know you've already checked this and I dont have Bezdek, but Peterson notes on p.119 that in the ordnance manuals of 1841 and 1850 the mounted artillery officers were to wear the same sabres as the enlisted troops of the light horse artillery M1840, but with ornamental gilt mountings.
This example surely seems much more ornate than most Civil War period officers sabres I've seen, especially with as you note, the hilt entirely cast.
The blade is if course from the well known Horstmann & Sons house in Philadelphia, the military outfitters who were in business long after the war.
While the simple stirrup hilt pattern of the M1840 light artillery sabres were known in both North and South, you're right, I doubt if the South had Philadelphia blades!!
Nice sword, looking forward to Dmitry and Glens comments
as always as they have stockpiled treasure troves of key notes on U.S. swords.
All the best,