I did an LS swap using an LMC suburban fuel tank and made my own custom fuel pump pickup and mount with a Walbro tank. I ahd a few rings cut to allow me to weld this to the tanks and bolt it together using a gasket I got from Tanks INC. I had a bunch made as there was a minimum purchase. I had the start holes CNC to a 16 bolt pattern.
I am looking to get $15 shipped in the US. These come with centering drill holes for you to drill them to the size you require. They are 0.250" thick and measure 5.5" OD and 4.5" ID.
I have a few of these, let me know if you are interested.