Going to be cleaning up some of my rigging this winter and will be making the switch to AN fittings and braided lines. What size AN line do I need to feed a mild 350 with a 650 cfm carb?

I would use #8(7/16) but you'd probably be fine with #6(5/16).

#6 is fine

Just a note for you AN and braided lines are NOT coast guard approved. I know it sounds stupid but I did the same as you and put nice AN braided hoses and surveyor and insurance say nope : ( You can have the lines on the carb and lines mounted on engine, but after that its silly double hose clamps and rubber USCG approved hose lol.

I too used an hose on.my Baja, coast guard never said a word when they inspected it although its illegal technically

I believe there's a push-on hose available that's USCG approved when properly clamped. Orlandi posted the part numbers once.

push lock hose to AN fitting .........I think most if not all braided is a compression type fitting

If you do go with braided stainless hose, use the Teflon lined hose. It holds up better to fuel than he rubber lined hose. Also the ID of the teflon lined hose is a bit larger than he rubber lined ss hose

Doesn't have to be clamped but it must have the yellow washer on the hose end.

Best thing is when they ask you if the blowers work and you turn them on to show that they work and they do. But there is no hose on the blowers. Just mounted to the transom and wired.