Until I can get on my computer, so I can elaborate more, I came up with an idea. Why not "glue" a bracket to the bottom of the tank so the pump will sit below the tank and use the drain port to feed the pump?
The drain port is a 1/8" NPT pipe plug so I'll have to feed the pump using a 5/16" fuel nipple then use a 3/8" outlet coming off the pump to feed the fuel line above the sending unit. Then just cap off the port on the sending unit.
The line coming off the mechanical pump is 5/16" anyway.
My theory is since an electric fuel pump will flow more, eventually the line will fill up with gas when the float valve is closed.
Since this is not a high performance 302 engine (2 barrel Autolite at that) I doubt fuel starvation would be an issue.
So what about this glue? I have used 3M structural adhesive, RTV and if it has not dried up I've got a tube of some 3M urethane leftover when I glued the windows into their tracks.
Just get the surfaces down to bare metal, apply it and use a sissor Jack to hold it in place until it cures . I've actually done this before.
See where my finger is pointing. This is where I want to mount the pump. Only issue is I need to be careful and not hit something and rip it off since the car is lowered.
I pulled the plug out and gas shot out like gangbusters.
Only a bit of crud came out. Not bad for a 51 year old car.
Also I took a photo of a fuel pump I mounted on my turbo Yugo if you can see around the cob webs. This car has been off the road for sometime.
Its a GM throttle body pump. More on that later. That was mentioned as a suggestion. That is a story in itself. I'll comment on that later.