/jp/ - Otaku Culture

I've got a few questions regarding this page

1.
>今の下だろう

I'm guessing 今の is an abbreviation for another word because の can only be the subject particle in relatives clauses, and "under of now" doesn't make sense. What's the use of の here?

2.
>ヒモの下だって

I'm guessing this isn't だって meaning "too/even/because" and that it's just ヒモの下だ with って signifying that this is what he observed/saw, is this correct?

3.
>上だっつーの

In Tae Kim's "Casual Patterns and Slang" lesson he gives examples of っつうの meaning like an exasperated "I said X" but I'm not sure where this comes from. というの doesn't have this meaning, so should it just be considered a separate expression? Also, とーちゃん is making that statement for the first time (he's not repeating himself), so I don't know how any statement like っつうの meaning "I said ~" would be valid.

4.
>通ってだな

What is this? I'm guessing he's just using 通って to mean "go over-and" and だな as a verbal pause before explaining the rest in the next panel, is this correct?