Two Flints, those carbines are among the many SRS mysteries. They appear with dates around August of 1863. But(!), the first Spencer carbines weren't delivered until October 3rd of '63. That's when the the inspection certificates arrived at the War Department, so the guns were probably actually delivered a week or two before that, but August is out of the question.
Frank Mallory did the SRS research, and reported several of these sorts of anomalies over on the Trapdoor collector website
www.trapdoorcollector.com. He said then that most of the records he was searching through were War Department copies. He knew the clerks were making mistakes, but rather than compound the errors with assumptions, he copied exactly what the records showed. In all likelihood, the copyists were bored to tears, and wouldn't have known a carbine from a rifle anyway. All the other cavalry had carbines, so the 11th Ohio got carbines too. Another possibility is that the unit is the 11th Ohio Mounted Infantry. MI units were often reported as cavalry in the records, and would have been issued rifles, so that would be a double transcription error.
The other units with low number carbines show up in late 1865, so they are probably M-1865s, not M-1860s. What's even stranger, the 1st Ky. Cav., which is reported as having low number carbines in December of '65, mustered out in September of '65. The record might be for the 1st Vet. Ky. Cav. I can't find a history on them, but if they had Spencers in December of '65, they were probably sitting in Texas waiting to throw a party for Mexican Emperor Maximilian, who wisely decided not to come.
The 19th Pa Cav. also has a bunch of Spencer M-1860 carbines with impossibly low numbers (as low as nr.
. Unfortunately, there is no date on the survey. The first 750 Spencers were Navy rifles (serial numbers below 1000, but delivered just after the 5th and 6th Mich Cav. rifles, serial numbers mostly between 1-2000). There is no way that the 19th Pa. got M-1860s from the Navy! The 19th did stay in at the close of the war and served in Texas and later La., so they could have gotten M-1865 carbines. Here's another strangeness, most of the first couple thousand M-1865s are rifles. I have M-1865 rifle #1221, with the matching number under the barrel, while the 19th Pa. shows 1220 and 1222 as carbines.
Also, I've never seen records of Spencer or Springfield rebuilding M-1860s as M-1865s. The receivers and barrel contours are quite a bit different, so such a gun would be easy to identify. An M-1865 rifle cut down to carbine length does have the same barrel contour as an M-1860 carbine, and some very early M-1865 carbines have 22" M-1860 barrels bored to 50 cal. with 6 grooves. One in the 7000 range shouldn't though. The Springfield M-1860 rebuilds are sleeved to 50 cal, but are not marked "M-1865". Springfield rebuilt and refinished a lot of M-1865s. These are marked "M-1865". With M-1865s, the barrels were not sleeved. If they were not serviceable, they were simply replaced. Rebuilt Spencers were considered second class arms and were rarely issued to front line troops. They usually went to militia, teamster, scouts and so on. If there is an ESA cartouche behind the sling bar, the gun has been through Springfield.
Life in the Spencer world is very odd sometimes.
If it doesn't heat up too much this afternoon, I'm going to get out and shoot mine!