These lenses were made by the UK lens makers at the time; Dallmeyer, Ross London, Wray, Aldis, etc. Almost all of them have pretty long focal lengths, and the 5 inch f4 is probably the widest lens it used. In large format, 5 inch (roughly 120mm) is actually a wide angle! The 5 inch f4 looks strikingly similar to the Ross London 5 inch f4. I wouldn't be surprised if they are the same lens.
I haven't tried them yet. The 5 inch f4 seems easy to adapt, so maybe I will try that one first and see how it performs. I won't put too much hope on absolute sharpness/contrast, but I am hoping it will have interesting rendering characteristics.
The Air Ministry Lenses - 8 inch f5.6 on left, 5 inch f4 on right. Click for larger.