A Walbro pump is the usual upgrade for intank pumps in the factory locations.
I was thining about the later EFI Suburban tank, but the 40 gallon is just too big and the 30 gallon requires moving crossmembers....
Check out my buld thread for a tank I was designing for my Chevelle...
here
Here is a surge tank that you could install into a custom tank....
here
This website also has parts you can use to build your own surge tank.... like check valves