So the first part, そうかそういや is preamble, "Is that so? come to think of it..." ペッパー is the name of the protagonist who's being addressed. But then I have trouble.
昔のユト: the Ute people from the old days? ユト, so far as I can see, is only used to refer to the Native American Ute tribe, which fits the context because this is a Western.
So I'm assuming they are the object of the next phrase: ないひとつ思い出せねえんだったっけ
But I can't parse this. 思い出せねえんだったっけ is obviously 思い出せる, to recall, but I can't understand this conjugation. The だったっけ ending is past tense copula plus the -ke particle to indicate the speaker is trying to remember something?
It's also confusing because so far I haven't seen any reason to think they are talking about the Ute tribe. The conversation thus far ran something like:
"So, Pepper, I got a message from the State Police. Some guy saw a $10,000 bounty up near Diamond Hill. It's Wild Job, a survivor from the Cassidy Gang."
"The Cassidy gang...?"
And no mention of "Ute"...
Here's a picture, so you can see the katakana for yourselves:
Having skimmed ahead, I'm now actually pretty sure it's actually a person's name, though what "Yuto" is supposed to be in a Western setting I've no idea...