Federico:
the number of the beast ]By the way i see that you (wyager) use a lot of transistors for driving your project. Don't you have a 74141 off hand?
ps. the optocouples i need, TLP627, are damn expensive
I was basing my project off parts I could get from digikey and I couldn't find any HV nixie drivers. The MPSA42s were only like 5 bucks for 25 IIRC, so I just went with those. I suppose after the shift registers and resistors and perfboard, the 74141s off ebay would have been cheaper, but it was a learning experience anyway. 
BTW, are the optocouples to protect the rest of the circuit from high voltage?