Hi, I'm doing the exact same thing on my 19 ft 1963
Airstream Globetrotter. I'd love to collaborate with you if you're up for it. My son and I are researching plumbing designs and part numbers.
I've refurbished the frame (replaced two crossmembers and replaced an outrigger), upgraded to a fiberglass coated composite floor and am now designing the plumbing before I put the belly pan on.
I don't always get notifications from this forum, so if you're interested in sharing notes e-mail me at email@example.com
My blog (for what it's worth): https://ps63airstreamrebuild.com/