If you want to do it from barstock then a digital subscription will let you access Stew Hart's article with drawings, a PM to him should also work. They can also be downloaded from MEM forum, search "Potty Popcorn"
Julius De Wall has his redrawn version of stew's engine free to download
If you want to do one from castings then Myers in thetates do a 1/2 scale one or there is a guy who casts from original Cretors patterns
Edited By JasonB on 23/06/2018 15:55:02