Dear Phil,
Have you checked Texas Confederate Pensions? There is a "James Mathews Parmer" listed from Runnels County as having received a pension. The application number for him is 26203. You can order copies of these pension applications at http://www.tsl.state.tx.us/arc/archmail.html .
These pension applications are multi-page documents with witnesses statements, medical records, health and death records, sometimes attached. The last pension app I ordered was about fifteen pages of information.
I noted you stated your g-grandfather was from the Lampasas region; however, Company "E" of the 20th Texas Cavalry was recruited in Henderson County. Are you aware of any connections to Henderson County?
Jim