The question here is whether the schwa vowel was pronounced in the modal verb would(e)st. The printer’s manuscript has the two-syllable wouldest; the 1830 edition has the one-syllable wouldst. This issue is generally discussed under 1 Nephi 20:5 for the two modal verb forms should(e)st and would(e)st. Basically, we find the following for these two words:
What we seem to have here under point 5 is a minor tendency to replace original -st forms with the biblically styled -est forms, at least in the first two editions. In the manuscripts, Oliver Cowdery struggled in one case over these two forms, but only in an Isaiah quotation (namely, in 1 Nephi 20:5, listed under point 1). Unfortunately, the only case where scribe 2 of 𝓟 is involved with this variation is here in 3 Nephi 27:3, where he wrote wouldest, but the 1830 edition has the expected wouldst. So we cannot independently determine what this scribe’s error practice might have been with respect to modal verbs ending in -est or -st. Similarly, we have no evidence regarding what the 1830 typesetter might have done if his copytext had had a modal verb ending in -est (the models in his copytext all ended in -st). This lack of evidence suggests that we should adopt the general usage here in 3 Nephi 27:3; in other words, the reading in 𝓞 was probably wouldst and scribe 2 of 𝓟 made the change to wouldest, possibly because of his familiarity with the biblically styled ending-est (the same tendency shown by the typesetters for the 1830 and 1837 editions). This means that for this passage the critical text will maintain the expected shorter form ending in -st.
Summary: Accept in 3 Nephi 27:3 the form wouldst, the 1830 reading, rather than wouldest, the reading in 𝓟; in this instance we adopt the expected usage for the Book of Mormon; this decision implies that scribe 2 of 𝓟 replaced an original wouldst with wouldest, perhaps under the influence of the King James biblical style, which has only wouldest.