I have not made one of these in the true English style. But good long narrow bows can be made from Black Locust, however you would not be able to go as narrow as with Yew for example. I would think a 70-74" ntn and around 1 1/4" to 1 1/2" wide would work well. And Locust is a good strong wood and very hard, I don't think it would be tough to get at least 100lbs out of it. I have BL bows way shorter than 70 inches long that are pulling over 60.
CP