I see that I've forgot to add the 14 LED current limiting resistors put between the display cathodes and the collectors of the segment driver transistors to the schematics.

I do actually have 220 ohm resistors there or else the displays would be very unhappy being driven to 5 volt vcc by a p-fet and to ground via a fully saturated small signal BJT.  There probably would have been 100+ mA thru each segment...

heh....  strange that you haven't seen the '595 before. In almost ashamed to use it since it's by far the most commonly used ic in the "arduino maker" community. ;-)

I'm doing basically that. But I've set the /OE permanently low (active) so they are always outputting data. But the outputs doesn't update until the latch signal gets a rising edge.

My original plan was to use 3-to-8 decoders, but the only ones I would locally was the '138 with inverted outputs, and that won't work unless I use Schottky's or the transistors will never be fully turned off making all segments glow faintly all the time.

That made me laugh. Glad I'm not the only one with a '595 aversion ;)

I'm from the pre-arduino/maker CD4017 days of simple port-expansion.  I even got a tube of those new-fangled 74HC4017's which go faster :)  If you use one of those, it's shameful *and* it gives away your age :-)

I always get stumped by the '138, too, unless it's used for an active low line (like inverted 3-state output enables for addressing things onto a bus).

Hmmm.  I hadn't seen the 74HC595 before.  Interesting part. You shift in a single high-bit to activate one of the columns, and only enable the output when the bit gets to the correct position?