4

It's short for 張り倒してやるわ. -てやる contracts to -たる. For the meaning of this やる, see What does てやる mean when it is not used for giving? and What does the word 「やったる」mean? This やらぁ is perhaps originally やるわ (where わ is a masculine sentence-end particle), but it's now fundamentally a distinct sentence-ender used by rough speakers. It's similar to やるよ, やるぜ, etc., ...


3

It is certainly a form of です, but it is a dialect rather than an archaism. According to this, using でがす is seen in Kanto region and up, but sporadically. Apart from real dialect, でがす is used to indicate unrefined character, which may be the case with the sentence in the question. A typical character is an untidy guy, maybe with beard, who is a 子分 type -- I'm ...


1

すっがら is equivalent to するから here. I'm not sure why か became が, either an accent from the speaking character or some touch to make it cute.


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