The only M. Dreyfus I find in two databases is:
Marcus Dreyfus
Enlisted as a Private
"G" Co. AR 1st Mtd Rifles Cavalry
Sources used by Historical Data Systems, Inc.:
- Index to Compiled Confederate Military Service Records
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His CSR found at Footnote records:
Marcus Dryfur/s, age 17, enlisted as a Private in Captain Porter's Company,Churchill's Mounted Rifle Regiment, Arkansas Volunteers,* June 15, 1861 at Fort Smith by Captain Porter for 12 months, discharged September 10, 1861, no further records [Note, I would assume he was discharged for being underage]
* This company subsequently became Company G, 1st Regiment Arkansas Mounted Rifles
M317: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Arkansas