Have you ordered a copy of her pension application from ADAH in Montgomery? Those applications often contain some gems. There were at least three organizations known as the 4th Alabama Cavalry. Based on the widow's application coming from Wilcox County, it is most likely that he was in a company that eventually became Company A, 4th (Russell's) Cavalry. His company would have originally been Company B, 3rd (Forrest's Old) Tennessee Cavalry Regiment under Captain W. C. Bacot. If your date of death is correct, he died before the company became a part of Russell's 4th. In any case, I could not find a CMSR for him at all. This is not unusual for these units of cavalry. Go to this link and read the often confusing history of this unit. Read in particular the paragraph that starts, "Shortly after this date......." The first sentence or two should give you an idea of about where he died if he was with the unit at that time.
http://www.tngenweb.org/civilwar/csacav/csa3forrest.html