Hi Dan,
As luck would have it I have my original coil bracket from my Mark 1A off and am about to paint it. Waiting for a little drier weather. I am not sure if it would be oem to a 1965 Tiger.
Your gray coil bracket with the cinch bolt looks almost identical to mine, except that it has both tips angle cut. Also mine has a hole in the top, for some unknown reason. A 5/16 bolt fits very snugly through it, in a quick test to determine size. (Same as the non-mounting hole size in the center of the bottom part.)
FWIW, when I went to put a Pertronix coil in it, the coil fit a little loosely, even when cinch bolt tightened. I ended up putting a piece of sheetmetal, trimmed to size to fit in the upper part of the bracket to take up the extra space.
Hope some of that is helpful.
Gene
BTW, the cinch bolt is one of those that has a thin head and a little thin raised edge around the top at the outer edge of the hex, if that detail is important to you. Not sure how well something like that would photograph.