I've been dying to do this trip as well. My plan is to take my Dart, on the 100th anniversary of Route 66 in 2026, on the route as much as I can, all the way to LA, then up the Pacific Coast Highway, to San Fran, and return along US Route 50 all the way back. There's a website that has the updated version of Route 66 that are still open, I'll see if I can find it.