There's a business that builds high-end Advanced Design trucks here in Phoenix called Apicella Design. They show a LS header for an AD truck on their website - they say it is from Doug Thorley. (note that Apicella uses a TCI chassis on their builds so I don't know if it would fit a stock chassis or not)
https://apicelladesigns.com/engine-packages
You might call Doug Thorley Headers and ask. They also sell DIYkits.
http://www.dougthorleyheaders.com/thydiy