There has been a tendency to add the past perfect auxiliary had before believed in this passage, but the text seems to be consistent here by maintaining the simple past-tense believed. In verse 7, had was added in the 1874 RLDS edition (but then removed from the RLDS text in the 1908 RLDS edition). The source for the intrusive had was probably the had in the following relative clause, “which had been spoken by Alma and Amulek”. And in verse 8, Oliver Cowdery initially wrote had believed in the printer’s manuscript, but then he crossed out the had, probably because the original manuscript (no longer extant here) had only the simple past-tense form believed. In this instance, Oliver seems to have been influenced by the use of had in the following conjoined predicate: “or had been taught to believe”.
Summary: In accord with the earliest textual sources, maintain the two simple past-tense occurrences of believed in Alma 14:7–8: “who believed in the words … and whosoever believed”.