I just emailed you Leonard Neumann's chart. I refer to it when I have to make a venturi for an offset spraybar, like TT's, ST's, and some others. In general, I always use a .157" spraybar and a .272" venturi will work fine from .25LA to .46 LA and beyond. The reason I always use a .157" spraybar is because I don't like OS NV Assy., and by using a .157", I can use a lot of different brands...but usually Randy Aero's.
Unfortunately this chart is incorrect, and it's based on incorrect assumptions, specifically, that the choke area should be somehow a simple function of the displacement. It isn't. It will tend to give an abnormally small venturi size for small engines, and oversize venturis for large engines. You only need the small end, particularly, if you turn the engine abnormally slowly, which will cause you to use a very large prop with lots of pitch.
On the other hand, a .272 venturi with a .157 (ST) spraybar is right in the normal range for venturi at .0178 square inches of choke area. The normal range is around .0175 to .0190 square inches, and it's not a straightforward relationship to displacement. I think Dave won the 2008 WC using something a little smaller than .0175 on a 75. The smaller engines tend to the high end - not that the 75 wouldn't work with .0190 or larger, it's that you can't figure out how to get rid of all the power that would provide.