Steve,
I know these didn't all come with the same size jet. I'm sure you gave me correct information for 72.
I know there were very slight variances of the volley 1920. But I have no idea why there are so much variance in jet size.
I am comfortable putting the original jet size back in for some reason. I know all slant sixes were almost unchanged through the years for the 225 other then slight here and there. My 81 never came with this carburetor but I love the simplicity and how it is running. I hope I didn't sound as if I was brushing anyone's advice. I will be glad to use a 50 jet if my engine is happy. Being some of you are curious about my mileage improvement as I am too. I will fill her up tonight and calculate it and report back. Check my plugs and likely order some more jets.
Sorry for the long winded post.