The more changes made, the greater the risk of a mistake, so only the most needful changes where made; Because there is allot of time invested in the enclosure designs, no changes where made to the dimensions of the board, mounting hole locations, etc.
One change is to the Real Time Clock; The Rev A board was laid out with the intention of providing the super-accurate TXCO as an option, consequently, there was a separate DS1302 Real-Time Clock could work with just an lower-cost, external 32khz crystal, *or* be driven by the DS32KHZ TXCO. As it turns out, the TXCO was used always. So the Rev B boards will replace the separate RTC and TXCO with a unified part, the DS3232.
Another change is that I am adding a N-Channel MOSFET to drive one of the LED lines, and I am adding LEDs underneath each IN17 tube. The Rev A boards also had LED driver lines which were never used. External boards can also be fitted with LEDS and be driven with this line.