Yep, I did the same (modified stock sender to hang an EFI pump on it) and no complaints. I let the 5/16 tube stay in place (the old carb's feed line) as a return, unsoldered the 1/4" return, drilled the hole to 3/8 and bent some tubing.
Every V8 with EFI that I'm aware of came with 3/8 feed and 5/16 return. I don't need any other reason to do it that way, too.
When in doubt, imitate the OEMs as best you can.