Hi Robert glad to hear of someone with kindred desires i once had a 1923 Ner-a-car frame sans engine I fully restored the old frame then made new rims for the wheels when it came time for the engine i managed to purchase the original Sheffield motor plans i got as far as modeling up a wax copy of the engine casting but at the time lacked the time to make a casting then my whole project ended when I had to move and leave behind the works.
i don't know your skill set or available equipment and technology. but a real good place to start would be research for factory build plans on your proposed build. then think about if you do not already have them build a small set of foundry tools and equipment
But first off create a build in progress topic in the homemade creations or possibly one of the other forums for the tools you will need to make for your engine project
good luck