Somewhere I have a book on the history of the clay pits on the south bank of the Humber, and it contains a lot of detail on the keels and sloops. I'll try and dig it out, as I'd like to read it again.
If you want to see a couple of sloops in the flesh, The sluice at South Ferriby is where to head for, but they're only about during the summer months.
Try posting on the Dutch Barge Association mail list at www.barges.org. There is a member there (Tony Woodward I think) who has re-rigged his Humber Keel "Daybreak."