I assume it is impossible to use in-17 boards with in-14 and/or in-19 tubes... right?
Is there any existing (preferably cheap) boards for 6 nixies the size of in-14 with no separations?
That's the kind of board that can save a wiring headeach, and I don't like headeach...
No, not impossible at all! All you would have to do is connect the pins from the other style nixie tubes to the board in the correct spot. Use the IN-17 board for the multiplexing section of wiring diagram, so to speak.