The Book of Mormon manuscripts show a frequent tendency to mix up behold and beheld. Here in 1 Nephi 8:9, while copying from 𝓞 to 𝓟, Oliver Cowdery initially wrote behold, then immediately corrected his behold to beheld (the reading in 𝓞). As discussed in the previous variant, Oliver initially missed the subject pronoun I (which had been supralinearly inserted by scribe 3 of 𝓞 as a weakly written lowercase i ); thus Oliver may well have been expecting behold rather than beheld immediately following the after-clause.
Oliver Cowdery created the very same error later on in this chapter:
The 1830 typesetter rejected Oliver’s behold and restored beheld, but apparently without reference to 𝓞.
Interestingly, in both of these cases Oliver Cowdery originally created in 𝓟 a Hebrew-like behold-clause:
In these examples, behold is followed by noun phrase, not a clause (although an existential clause seems to be implied: “behold there was a large and spacious field”).
In the King James Bible, we can find examples of this Hebraistic literalism:
But the original text of the Book of Mormon does not actually have any examples of this kind of Hebraism, although Oliver Cowdery does seem to have momentarily created a couple of them.
For other examples of where behold and beheld have been mixed up, see Alma 34:6, 3 Nephi 1:15, and 3 Nephi 17:5.
Summary: Maintain the simple past-tense form beheld in 1 Nephi 8:9 and 1 Nephi 8:26.