Hi Eternal,
I guess I should have known about the fuel tank vent breather pipe for some unknown reason
Very similar tank to mine...
I know you mentioned you are going to fit a one way valve to prevent vaccum but are you also planning on fitting a vented fuel cap?
If you do weld a nut to the top of the tank keep it as near to the fold as possible as this will help prevent distortion to the top of the tank.
Would it be possible to make a bracket from the Mazda fuel tank sender cover picking up two of the bolts, just a thought.
Anything you weld to a fuel tank increases the risk of a leak or failure in the future.
Also I know you are aware but IVA requires an earthing strap from the fuel tank to the chassis. Iguess you could do this from the sender flange as well.