Edit: The OP has provided additional information which has changed my answer. What you see now is the new answer. Old answer is further below for reference.
Thank you for providing additional information. With more context, the translation changes a bit.
Note that the conversation in the first page (on the right side) indicates that there was a tension-breaking moment between the two, where the man in the black coat (hereinafter Black Coat) said to the man in the white coat (hereinafter White Coat) "That's fine, you do what you think is right, and I'll do what I believe is right." Then you can see at the last cut in the first page that White Coat has relaxed considerably, and is now playfully basically saying "Dude, you say that now but don't go getting all pissed off and telling me to get out of your way later, aight?"
Right afterwards is where the conversation you quoted in your original question takes place. Here, White Coat is playfully lamenting the fact that he no longer feels as tense as he did moments before, which is kind of unfortunate because he was just at the right place where he wasn't overly nervous but he was in high gear and ready to go kick some ass, and also laments about the fact they are still friend despite being polar opposites, which he obviously doesn't actually mind.
White Coat's monologue there roughly translates to "Man, I feel so stupid now (Because he was all worked up, but now the tension's gone). I was in a good place, too (He was in high gear and ready to kick some ass). " Then he thinks to himself, 'But that's fine.' Then he says, "Dude… Why are we still even friends, anyway? We're like polar opposites. You know what, never mind, whatever. Let's go have a XXXX (An after-party, maybe? I couldn't see the 漢字here, resolution was too low)" The dialogue that follows is evidence that they are no longer feeling tense, since they are discussing going to McDonalds after "cleaning up" aka kicking ass. Note that 「まったく」 in this case is a comment on its own and not a part of another sentence, an expression of lamentation like "Man…" "Dude…".
Old Answer:
To be more accurate, 「具合」 in itself merely refers to a condition or state of being. 「いい具合」 can be translated as being convenient, lucky, healthy or happy depending on the context, but what it literally means is "a good condition" or "a good state of being". So let's try and apply this to your specific situation.
"(I was) nervous in a good state of being/condition"? Somewhat awkward, but you can get a grasp of what they are trying to say. "(I was) nervous, but in a good way."That person was nervous, but not in the nerve-racking, anxiety inducing kind of way, but in a more positive way, such as waiting to see what gift your rich grandparents bought you for your birthday.
From the conversation you provided, it sounds as if the two were anticipating something good happening, but unfortunately it did not pan out and now they are playfully taking jabs at each other for it ("Dude, why are we still even friends?") in a way that only close friends can do.
