If anyone runs in to a similar predicament where they need to replace the overflow tubing to and inside the bottle, there is a locally sourced solution (instead of just grabbing some fuel line to replace the hose, which I imagine would be OK but I don't know its temperature rating).
Prestone sells a 2' length of 5/16" ID hose at Autozone and O'Reillys, part number RT0516. It's specifically called "radiator overflow tubing". Cost me $1.99.
It has an alternate part number of 65099 that when searched at Amazon.com comes up with a similar length of Goodyear product.
It fits perfect and looks OEM. Even uses the OEM spring clamps with no issues.
Cut the length TO the bottle to about 390 mm; cut the length within the bottle to 240-250 mm.
Thanks!