I came across the details that refer to the pictures below….part of Stuart Waycott’s 600cc ISDT Velocette outfit from 1936.
From p.251,... Phil relates...( and he was working for Veloce Ltd at the time)"…I gradually became landed with the job of supervising construction of the (ISDT) outfit for which Harold Willis agreed to provide a de-tuned Senior TT engine, bored out to 85mm, and with new flywheels giving 105mm stroke, bringing the capacity up to 596cc. As with its huge cylinder head and long stroke the engine was too bulky to fit into the old frame, another was made with a heavier top tube humped in the centre to clear the head.”….
Now on one of my several visits to “Owls Rest”, Phil’s property in Warrandyte, Victoria, we spoke of this incident above, as I had brought along two photos of the Waycott 600 outfit for his comments, .. these illustrate this article and he excitedly explained the above adding that he found the brain wondrous, as he had looked at the top area of the tank and fingered the spot with the index finger of his right hand, while placing his left index finger under the tank bottom ( and not visible to him) shuffling the two around until the finger underneath was directly over the spark plug end and had an assistant carefully mark these spots with chalk, then two holes were cut and they were in line with each other and a tube could be welded in as mentioned above. The brain of course can spatially adjust to this.
Left click on photos to enlarge.