1. As I noted previously, the SC2 can appear in poetry without the waw which usually accompanies it in prose. The same is true (and this is more widely accepted) of the PC2, which can appear in poetry as the type wayyiqtol, as in prose, or simply as yiqtol. Examples are ready to hand, such as Ps. 24:2, כי הוא על ימים יסדה || ועל נהרות יכוננה , "for he founded it (the earth) on the seas, and made it firm on the rivers." The past orientation is clear from the context, which deals with the creation of the earth. Other examples are Deut 32:10-13, Ps. 18: 4-19; etc. (There is an excellent post here on this very verse, with stimulating discussion in the comments.)
Another example, precisely of the same sort, is found in Ps. 78:58: ויכעיסוהו בבמותם ובפסילים יקניאוהו. "They angered him with their high places, and with their images made him jealous." Only the most captious or over-subtle interpreter could find a difference in the time reference of the two verbs here.
2. More controversial are examples of the opposite kind, in which verbs vocalized as preterites (PC2) must be understood as PC1 (imperfect) or jussive (PC3). This entails a rejection of the Masoretic vocalization, but the overall implicature of the poem, along with lexical and syntactical cues – in short, the context – make such a move necessary in many cases. An example is Ps. 94:23: וישב עליהם את אונם וברעתם יצמיתם. "May he turn against them their sin, and destroy them for their evil."
In this case, the first verb wayyashev must be understood as PC3, not PC2. The LXX translates both verbs in the future tense (see the BHS apparatus). Another example is Ps. 29:9, where וַיֶּחֱשֹׂף must be understood as PC1, in accordance with the sense and form of the verb יְחוֹלֵל in the previous line. Here also the LXX translates the first verb as present participle, the second as future; note also that the targum translates both by participles.
To sum up: in Biblical Hebrew poetry, the form known as wayyiqtol (preterite) in prose can be simply yiqtol in poetry, but still a preterite. On the other hand, forms that the Masoretic text presents as wayyiqtol preterites must sometimes be understood from the context to be imperfect or jussive with conjunctive waw (and therefore the MT must be vocalized differently).
I think these principles are fairly uncontroversial. I'll try to get to more debatable ones (e.g., the prophetic perfect) sometime in the near future. In the meantime, comments are welcome.
