The 1874 RLDS edition replaced the plural abominations with the singular, but the 1908 RLDS edition restored the plural to the RLDS text. Not only is the plural the earliest reading here, but surrounding usage in this verse supports it:
In fact, the use of such in the second conjunctive phrase (“such wickedness and abominations and murders”) directly connects that phrase to the preceding conjunctive phrase.
Summary: Maintain the plural abominations throughout Alma 37:29.