The key point everyone is overlooking is the files contain no carriage returns. That is, it sounds like the text files are just one long line that cycles through three fields of length 15, 12, and 30.
You can probably use any text editor with a fixed width font, if you turn on word wrap and resize the window to be exactly 57 characters wide. You probably also want a text editor with overtype mode, so the fields will stay lined up as you edit.
(Edit: As I commented on Mush's answer, WordPad might work with the following setup. Go to View, Options, Text. Select "Wrap to ruler" and check Ruler so the ruler is visible. Then drag the right margin triangle in the ruler until you get the text to wrap at exactly the 57 characters you need. Also, press the Insert key on the keyboard to turn on overtype mode.)
A hex editor might work, if you can set it to exactly 57 characters per line. I have XVI32 on my computer, but even at the smallest font size and with the address column turned off, I could only fit about 45 characters per line on my 1024 × 768 screen. If your screen resolution is larger you may be able to squeeze in the 57 characters you need. The problem is XVI32 always shows both the hex data and text data, but it sounds like you're looking for a similar editor, but just need the text view.