I am very glad that a link was provided that leads to the text copy of the Hasluck book. My interests are in building the engine only, and not the bike.
Regarding the engine-fabrication section of the book:
The book goes into great detail about how to machine the commercially available, 1906 castings for this engine. The majority of the text is written for the times, the terminology is difficult to understand, and, is mostly archaic. Our modern tools, and machining methods would be used instead of the methods used back then.
If you are going to build this engine from bar-stock and weldments, about 75% of the written text is useless, and has nothing to do with the engine that is being built in this thread. Granted, the engine in this thread is derived from the textbook design, and some of the parts and measurements may be the same, or, very similar, but the modern version just "looks" old-fashioned.
I am very glad that I did not have to order the book and then be ultimately disappointed after reading the engine chapter. By the way, there is a smaller, and lighter version of this engine-type in later chapters. The directions will give you and engine with a 2-1/2" bore and stroke.
If it's the modern version of the engine that you want to build, follow this thread closely. The book will not fill in the blanks....unless you want to wind your own spark-coil, and make a spark plug. I'd rather go to the store and buy them...but hey, that's just me. I'll follow Tom's way.
Just my opinion.
Frank