Hi Ben,
I don't know if you've seen Ken's website so here are some links:
http://www.jkwynn.co.uk/
http://www.jkwynn.co.uk/66_HTML/66_Thumbs.html
http://www.jkwynn.co.uk/Project_Images/66/66_XOver.pdf
The last link has a parts list and a very nice diagram.
Here is a link, to our own "Knowledge Cafe" for the Ditton 44 circuit diagram and parts list:
https://theartofsound.net/forum/show...er-Information
You'll see there are some differences.
Tweeter (Ditton 44 - C1, C2, C3, C4 / Ken's 66 - C5, C6), disregard the 44 circuit and follow Ken's work. It's only a matter of getting the correct value e.g. Ditton 44 C1 + C2 (4.7 + 1.5 = 6.2) Ken's 66 C6 = 6.2. Ken's approach is arguably better and it's definitely cheaper.
Midrange The only difference here is a change in value (Ditton 44 - C5 = 6 / Ken's 66 C3 = 4) for this, stick with the Ditton 44 https://www.falconacoustics.co.uk/al...le-series.html
Other than that, follow Ken's work, that's all I did!
As for Quad 405's. If you click the link in my signature it will take you to my Gallery. On the first page there's a link to what I did with them, best of all the photo's were uploaded here, not PhotoFuckIt so they're still visible! Other than that I can't be of any more help I'm afraid, read through the thread and you'll soon realise I'm not even at novice level
I do hope this gives you the information and confidence to get this started, if not just keep asking questions till you get it