Rowland's "Military History of MS" lists company officers of the 8th MS and shows that Richard P. Austin was, in fact, one of four captains of Co. B, the "Pinckney Guards." Richard was apparently previously a second lieutenant in this same company.
Sadly, period regimental histories are rare. Contemporary company-level histories are almost unheard of -- unfortunately.
There is, however, a capsule history of this unit on the MS SCV site at www.mississippiscv.org. Click on "Research Help."
MS CS Graves Registrations shows:
"AUSTIN, Richard (Dr) 8th MS Inf. 1835-1898 Copi Scot," meaning that he was born in Copiah County, MS, in 1835, died in 1898, and is buried in Scott County, MS.
According to MS CS Pension Applicatons, "Mrs. R.P. Austin" filed a Confederate Widows Pension Application in 1915 in Scott County, MS. In that application, she states that she was the widow of "R.P. Austin" of the "8th MS."
(See www.mississippiscv.org for further info on MS CS Grave Registrations and MS CS Pension Applications. Click on "Research Help.")
Wish I could have supplied more! -- Jim Huffman, Gainesville Vols