The conflict in number agreement for “the heavens is a place” has led to a couple of emendations in the text. In his editing for the 1837 edition, Joseph Smith changed the singular verb is to are in 𝓟, but this editorial change was never implemented in the 1837 (or any later) edition. This change may be grammatically preferable to the current reading (“the heavens is a place”), yet both readings are awkward because of the inherent clash between the heavens and a place. (Compare this example to the difficulties with a sentence like “Scissors are a handy tool”, which nonetheless in standard English is clearly preferable to “Scissors is a handy tool”.) There are two passages in the text where the subject heavens takes plural verb forms:
Of course, in both these cases there is no conflict between a plural subject and a singular predicate subject (as in Alma 18:30). On the other hand, there is one passage where the singular pronoun it is used to refer to a plural heavens:
The it works here because the corresponding subject complement is the singular his throne.
An alternative solution to the conflict in number between heavens and a place here in Alma 18:30 has been to change the plural subject heavens to the singular heaven, as in the 1874 RLDS edition (and followed by the second RLDS edition in 1892): “the heaven is a place”. But this change has its own problems since at the end of the preceding verse king Lamoni says, “but I do not know the heavens”. Of course, one might try to change this preceding occurrence of the heavens to heaven. In fact, the first occurrence of heaven(s) in verse 28 is already in the singular. Thus a “consistent” editing to the singular heaven would read as follows:
Of course, this solution also produces its own awkwardness: namely, “but I do not know the heaven”. Even changing the heaven to simply heaven (by omitting the definite article the) would not help particularly.
In accord with the reading of 𝓟, the 1908 RLDS edition restored the plural heavens here in Alma 18:30. The critical text will maintain the earliest reading, despite its awkwardness (“the heavens is a place where God dwells and all his holy angels”). In the standard edition, the text could be grammatically emended to “the heavens are a place” (Joseph Smith’s emendation in 𝓟). For a complete discussion of this grammatical problem, see under subject-verb agreement in volume 3.
Summary: Maintain in Alma 18:30 the subject-verb disagreement that is found in the earliest extant reading: “the heavens is a place where God dwells and all his holy angels”.