an fittings

If you don't want to re-do the lines, go from the -8 to a small segment of line with -6 fittings. There are adapters to go from -8 to -6 and then -6 to 5/16.

The RobbMc pickup in my tank has a -8 outlet but I step down to a -6 fitting and run 3/8 lines. Works fine. Can't vouch for the double step down though, I wouldn't do that myself.

AN fittings rule though dude. Every single hose barb/worm clamp jive line on my car leaked. EVERY one. Replaced with lightweight push lok hose with AN style fittings - no leaks. Looks cool too.

That being said, if you're gonna spend a bunch of coin on lines and fittings that you hate, just pop for a new tank and be done with it. You can probably get a used one for cheap. New ones can usually be had for under two bills if you don't care where they are made...