Here check these out.
https://www.boatid.com/moeller-marin...SABEgLg9PD_BwE
https://www.westmarine.com/buy/moell...iABEgLr9fD_BwE
I found one molded with the 2 right next to each other., can’t remember where now. I’d imagine it’s not a critical design (vs a best practice), as the vent deals with vapor locking and the filler is fuel.
My factory originals look like this: the fill and vent hoses are next to each other and makes the lengths required identical. but the tubes themselves enter the tanks at different points. Note the fill and vent are bow side, the pick up are stern side. I heard about a guy here on islands who put his tank in backwards with pickup facing bow. Lost prime when he had plenty left b/c he didn’t consider being on plane etc…
However, I’d guess that while it makes sense from a manufacturing perspective (cheaper materials and molds). it also makes the mistake of overfilling and it going out the vent a greater possibility. Is it necessary to separate..,no. But as you fill COULD you cause fuel to go out vent easier…seems likely. So us perfectionists would make one a different way than we would buy it and use either.
Just my thoughts.
I’d put the pickup towards the rear so when on plane I’m pushing fuel in direction it will naturally be forced. Filling and vent on mine are forward I think. Only concern is returns not being to close to pickup…if you have efi.