Mike: I found a great article by a local newspaper near where WW McIver's son lived that mentioned WW McIver dressing as a woman to spy because of his small build and long curly hair. Also mentions a run in with Jesse James. This link should take you there.

http://www.reporternews.com/news/2007/may/06/pcemetery-cleanup-renews-friendships-conjures/

Also found an obit for his son Clay that mentions the spy company:

Taps for PVT Clay W McIver
Clay Weldon McIver (Mac), 95, of Winters, TX passed away on April 15, 2009. He was assigned to the 349th Bomb Squadron, RAF Thorpe Abbotts, England.
He was one of the last surviving real Sons of the Confederacy. His father, William Wood (WW) McIver, was a veteran of Johnson's Spy Company, Texas Cavalry, during the American Civil War. Clay was a proud veteran of World War II and was dearly loved by his many friends and relatives.

My cousins and I would love any info that you could share. You can email me directly at donna@landmark-auction.com. Thanks.