Charles,
Ask the question re Bob's Shoestring engine on the "Open" (the main) forum and you'll likely get a lot more responses. These downline threads can sometimes lie dormant for some time.
Once you've got the weight of Bob's engine measure from the Shoestring plan's center of gravity to ~the front hold down bolt in inches (a rough approximation of the CG of the engine). Multiply that distance by the weight of the Bob's engine in ounces and get a result in "oz/inches". Then divide that number by the weight of your four stroke and the result will give you a reasonably practical location for the front hold down bolts on the four stroke.
By the way, 19oz sounds like a pretty big engine for one of Bob's "usual" ships although I'm not an expert on four strokes. You'll likely come out with a much shorter nose after doing the math and then might have an issue with tank length....Just a thought.
Ted Fancher