You won't need a larger line for a slant, but you will need something for a return line. You cannot use the 1/4" vapor line for a couple of reasons.......it's too small and IT IS THE VENT for the tank. You MUST keep it open, if you remove the evap vapor emissions controls
You can buy aftermarket senders with a second line. If you can fab, you could pull the filler tube out and weld/ braze a fitting into it.
I lean towards Holley. Megasquirt is something you might check out if you DIY a lot. Many people seem to like EFI tech, there are others