I saw your post. That will be a much larger challenge than what I've done. All I had to do was call Tommy for the base. Making one from scratch will be much more difficult than modifying an existing base. I'll keep an eye on your progress.

Anyone who has done a project that requires paint, will understand the WEEKS that I have not posted progress on the project.
I delivered the welded, finished? air cleaner base to my buddy who insisted on painting it, weeks ago. First comment, "take it home and blend in the outer edges for paint. I did that, then waited.
Today, I got to watch the paint applied to my project. You don't want to know how many hours he spent getting it "ready for paint" after I had spent days on it! But, the finished project is as perfect as it could get.

The air cleaner lid is next. It has too much Red in it. He has mixed an early HEMI orange to match the block. By weeks end, I should have it installed. Guess who is going to cut the hole in the hood to make it all work? Not me!!!!!!

Here's a template if you want to cut the hood like the original WO23.

https://www.ebay.com/itm/1966-1967-WO23-RO23-426-Race-Hemi-Oval-Hood-Template/253393614521?

Here's the plate, the seller is a Moparts member.

https://www.ebay.com/itm/1966-67-RO23-WO23-426-Race-Hemi-Underhood-Plate/253443293644?

OK, I finally finished the air cleaner. The rubber seal was too thick. I found a sheet of 1" closed cell foam. A customer was kind enough to water jet the gasket out. It is done. Except for the HEMI decal on the lid, yet to come!

The details are important. It is a rainy day here in East TN. I spent it putting the final touches on the only cold air system for a 66' with RO/WO23 hood scoop that has an air cleaner!