In my past builds I've just made my own mounts using square tube and flat bar stock, and use the factory clamshell mounts.
If you have to make the entire thing, including the rubber mount portion, this video has some good ideas as well:
https://youtu.be/6zKmUUM_d4c
If you're looking for a 'bolt on' or kit solution I can't help with that.
If you need a BOP to Chevy bellhousing adapter, they are widely available:
https://www.speedwaymotors.com/Speedway ... PYEALw_wcB
You might also have luck searching under the other B-body cars (impala, Bel Air, Caprice) for stuff that would work, sometimes adapters and brackets are marketed specifically for the popular nameplate but will also work across the platform with little to no modifications.
http://www.brphotrods.com/products/65-7 ... index.html