Here's a dimensioned sketch of the bracket. You already have the marks on your tank. My old broken solder flow fits correctly when the part of the bracket with the hole is at the southwest line of the little square in your photo, with north being at the top of your photo.
The standoff is 10 mm diameter and, according to my notes, 113 mm long, but that may be total length. I measured everything so I can identify stuff when it comes back from the CAD plater. Right now it's all at my restorers place, in a bucket. If I had to make it myself, I would use a piece of 10 mm diameter tubing (1/4 inch fuel line is close enough probably), mash the ends in my vice, drill the holes and grind the rounds. A little paint will make it perfect. You can also find the length by measuring in place.
Good luck, I hope this helps.
Tom Kizer