Beware that only a few of the narrowboats originally used had reliable plans made. The wooden boat builders like Nurser Bros. of braunston and Walkers of Rickmansworth just built from memory and a few pattern sticks.
Your best bet is to find a yard with some boats on hard standing and measure them yourself. Only the bow and swim (aft) have much shape to them. A boat would be at most 71'-6" long, more normally 70' and never more than 7' beam, widest. Some, like our old Nurser boat were built by request of the owners to 6'-10" beam to make life on the Welsh Canal easier. They had 5 planks of oak about 9-9 1/2" wide up the sides. Wooden boats generally had a more generous bow shape and swim and consequently move more beautifully through the water. "Joshers" had a very s-sectioned bow shape, but were unusual in that respect for steel or iron boats. Rivetted iron boats were more contemporary with the wooden boats before the War.
You could use a Hogg drawing as a basis and then overdraw onto it the essential shape of the particular, undrawn boat you have good photos of.
A model shop owner in Staffordshire called Alan (sorry, lousy memory for names) made a well measured model of our boat and was impressed by how well she swam.
Regards,
V
