My forum skills may be one of the ineptitude I mentioned in my last post. 
Anyway, Iām happy to see several replies since my glorified bump post. Iāll try to be more active.
Power supply regulation : I think I have this sussed, using an actively-controlled supply intended for flashlamps. I do, however, need to choose a couple of components carefully, as the voltage I am looking at is different from that for the components recommended in the datasheet.
āElectronic Digital Slide Ruleā article : Got a copy thanks to my librarian sister, although it took a while.
I had a bunch of things happen, including suddenly needing to drive a relative to Houston for a medical appointment (train service canāt get here soon enough), but things are looking up. There should be no problem using the 4527 CMOS BCD rate multiplier for the logic section, so I donāt need to worry about the power requirements of a TTL chip there. 5V CMOS should be just fine. A copy of Don Lancasterās CMOS Cookbook should be helpful (I have a PDF of the TTL Cookbook)ā¦ looks like the Fort Worth library has it, so Iāll pick it up when I head downtown to get my mail. That will probably be tomorrow, because USPS decided to route my Priority 2-Day package from Massachusetts via Anaheim, Californiaā¦
Glad to see there is still some traction. Sadly, I have no extra cycles to help you get to where you need to be, but I anxiously await burning a few cycles when ready to build. 
If you follow the following link through about four more links, you will eventually find some schematics for a Geiger counter kit:
http://www.electroschematics.com/12225/diy-geiger-counter/
I canāt claim that this information would necessarily be useful for the current project or not.