Yours is a very old posting, so hopefully you've gotten your answer by this time.
First, I needed to identify his date of birth and information to verify and also further check records. Often persons are not married where believed. I also found your posted family tree, it helps to post the link to your person so volunteers have all the needed research information:http://trees.ancestry.com/tree/20500995/person/957653105?ssr...
The tree shows you to be a very competent researcher.
A Horace J. Morgan, born abt 1917 (was 74 at time of marriage) married Sarah K. Youngkin, 58, in Nueces County, on 12 Nov 1991.
Your tree showed Rachel Marie Barrett, born 15 May 1918, died 22 Mar 2006 in Alabama. Rachel remarried to M.C. Phillips, 29 Nov 1908-13 Sep 1971.
I found a July 17, 1953 edition of the Corpus Christi Times concerning Horace. It identified him as a painter and former boxer. I did a screen shot and can email the article to you. My email is found by clicking my name in the top left of this posting.
--A May 18, 1947 edition, where he was questioned about his knowledge of a stabbing incident he had reported.
The State of Texas did not begin to collect marriage records until 1966, so you would have to contact the County where the marriage was conducted. If you KNOW it was in Nueces: http://www.co.nueces.tx.us/countyclerk/
There is a Public Records Search, you would have to register (free). I did not and do not know if the computerized records go back to 1955 (which I would doubt, but MANY counties across the country do have records online that far back).