Yerrrr Welcome!!!
I tried to be true to Bart's write up when I converted it to PDF (only took a little comic liberties). In retrospect, I should've added a hyperlink to his website so that any updates could be tracked. The PDF isn't supposed to do anything more than provide a copy for peeps to archive if they wish & print a throw-away copy to have in the garage whilst doing the repair.
Back on topic: Take the pix of the timing mark alignments to an authorized Isuzu repair facility (yes, those still exist) & find out if it appears out of spec to them.
IMHO, although the mark is obviously off slightly, it's not off by the amount that a 1 tooth adjustment on the belt would correct. If you adjust the belt by 1 tooth, the mark may actually be on the other side of the reference. This makes me think that it's a tensioner issue.
BTW, Chocolate Monkey: