Here’s the hardware you need to mount the buckets
https://www.musclecarparts.cc/shop/item.aspx/1968-1971-dodge-and-plymouth-b-body-4-headlight-adjuster-spring-kit/8069/?gad_source=1
oh wait a sec them are for 4 headlamp systems
I’m a 30 year electrician if that makes a hill of beans.
But I would clean the remaining tabs and make up new ones made exactly like the originals and solder them on top. I would not recommend you to drill the rivets because you will lose the clamping force on the connection.
Check the hose at the tank for leaks as stated above if that don’t cure it your probably gonna need to check the sending unit pickup tube if it’s the original. There’s a chance there could be a pin hole rusted in it an easy way to check that is filler up and see if the air disappears.
If your only doing an intake get some gasket remover some brands of it still have the good stuff in them.
https://www.appliedthermalfluids.com/product/loctite-sf-790-gasket-remover-known-as-loctite-chisel-paint-strippe-79040/