Since we follow print unless there is a VERY good reason not to, I think it’s fine here to just follow the print and use the centered headings as shown in print, with a blank line before and after each heading, of course. I don’t think it is necessary to start each preface on a new braille page if there is room for the centered heading and at least one line of text after the blank line. However, if the print page changes, you can insert the new print page indicator as usual.
–Joanna