Rana,
It appears that info on this unit is indeed, scarce. I was able to find the following:
at this website: http://members.aol.com/mapurdy16/GALegion.htm#FLGSG
It gives the Company, infantry or cavalry,the commander's name, and the county it was organized in.

Floyd Legion, Georgia State Guards
Col. James G. Yeiser
Co. A James H. Lawrance Floyd
Co. B Cave Spring Mounted Infantry Jackson Trout Floyd
Co. C Rome Cavalry Samuel D. Wragg Floyd
Co. D Floyd Rangers A. A. Terhune Floyd
Co. E Floyd Cavalry Marcellus L. Frankman Floyd
Co. F Chulic Mounted Infantry John A. Taliaferro Floyd
Co. G Polk Mounted Infantry Henty F. Wimberly Polk
Co. H Polk Volunteers Stephen A. Borders Polk
Co. I Forrest Artillery C. O. Stillman Floyd
Co. K Paulding Infantry James B. Dean Paulding
This legion was organized in August 1863 to serve for six months as local defence. The units was disbanded in February 1864.

As for J.R.Cowan, he is listed on the NPS Sailors and Soldiers website at: http://www.itd.nps.gov/cwss/

Cowan, J.R. Confederate Floyd Legion, Georgia (State Guards)

His CSR (compiled service record) would be available from the Dept. of Archives and History in Atlanta.That may contain some more info, but would not list any geneology records.

You may also want to check out the Floyd County Library site at: http://www.gagensociety.org/librome.htm
An inquiry to them may head you in the right direction.

.........Neal