Dave, the 1/4" BSC nut is where one side of the rear plate for the battery bracket is secured and the hole 1 3/8" from the RH edge of the drawing is one of the oil tank securing points.
That drawing is done from the oil tank side of the mounting plate.
This picture of the rear part of the battery bracket sitting on the oil tank mounting plate might help?
I drew that up about 17 years ago so it isn't flash - I didn't have anything other than Word to do it.
Let me know if you need any other details around the oil tank bracket mounting as it can be confusing with the rear mudguard bracket, the battery bracket and the three oil tank spacers.
Thank you very much Ray. I think I may be able to sort it out now, but if I have any other questions I will email you. Its a bit hard when you start a rebuild with just a box of bits. Regards Dave.