Well, it is amazing what some actual research will do

... In my pile of useless stuff is an OS engine book with ALL the numbers, circa 1993. And at some point in the forgotten past I had noted that the 10 FP venturi was a very few thousandths less than the 15 FP, and that they were interchangeable... And Leester you are absolutely correct about the 6mm size! The spraybar is .137 ....

So, looks like approx size of .235 will be about right!!
What it boils down to, I shoulda done more looking before I opened my dumb computer...

Thanks all!

Jim