Hi Keith,
Have you tried the Ironbridge Gorge Museum?, they had a big hand in the restoration of the Severn Trow ‘Spry’. I bought a book there, about the restoration, by C.S.Johnson and in the back are some very good line drawings (by Alan Williams) of the Spry. I also remember seeing a large drawing of the Spry on display along-side the actual boat.
Best of luck.
Mike.