The current Walthers Track turnouts are made from new tooling. There are two easy ways to tell whether a turnout is new tooling - Shinohara is not mentioned on the box, and the new turnouts have one-piece points.
https://www.walthers.com/catalogsearch/result/index/?manufacturer_name=20976&q=curved+turnout
LazersI have just laid an Atlas #536 24" Set-track over a #6 Shinohara (Scale Link) It matches the Outer-radius perfect. The Inner-radius matches Atlas 15" Radius Curve. An 18" is too large.
Meanwhile, I bought a new Walthers #6 from Hiawatha Hobbies. That purports to be 24/20, but there is reason to believe it could actually be 20/18. When it gets here, I'll find out if it's a tight enough curve, and if not, then I may go back to Scale Link.
-Matt
Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.