Inliners International Forums General Discussion Vortec 4200 header source

A company called OBX makes a similar header. Slightly cheaper, looks to be of the import variety, so quality may be an issue.

https://www.ebay.com/i/172344638870?chn=ps

Here's a flange for those wanting to DIY or make a turbo manifold.

https://www.racemufflers.com/Chevy-4-2L-Inline-6-DOHC-Mild-Steel-Header-Flange-p/rm2096-mhf.htm