Hello Ben, I was totally happy with the headers GP Headers made for me as well as all dealings with them. I made my own plug wires, all Moroso parts, details here.
It's a D9ZZ-7007-A block plate. I got it from Mustangs Plus, but they are closed now, owner retired. I did have to modify it to work with the Quaife bell housing.
A vent valve just like the one in the last photo in this post:
https://www.gt40s.com/threads/bryans-rcr40.52988/post-553672
So a total of four of those.
By measurement I calculated their volume at about 11.9 gallons if you could fill the entire tank including the upper section.
https://www.gt40s.com/threads/bryans-rcr40.52988/post-553134