PDP-8 CPU question

I brought home my PDP-8 yesterday. Besides the goodies that I got from Thom for it I also dug around in the stuff that he sold to the surplus store and found MORE goodies. Like a pile of H851 jumpers, a >>16k<< core memory board (and driver/sense board) for the PDP-8, a set of Plessey RK-05 disk drive controller cards for the PDP-8, some DEC PDP-11/34 Programmer's Panels. I also visited Thom and dug through some old GR manuals that he was throwing out and found an Engineering package for the MM8 core memory cards, some docs for the Centronics 300 printer, docs for a Dilog card and more. I also dumped all the GR docs from the LONG three ring binders and I'll keep them and put the long DEC docs in them. Thanks Thom! I'll post a list of the docs as I go through them and see if anyone wants to scan them and post them (Al?). Or I can post them if someone will scan them. (I just do NOT have the time to scan stuff!) Anyway I've been reading the PDP-8a User's Manual and trying to figure out what all I have here and I have a question about the PDP-8 CPUs. DEC offered two different CPUs for the PDP-8, one is the KK8-A which is a single M8315 card. The other is the KK8-E which consist of an M8300 and M8310 cards which are the CPU and an M8320 Bus Loads card and a M8330 Timing Generator card. Can someone explain the differences between the two and why DEC offered two very different CPUs for the 8? Can I replace simply the M8300/8310/8320/8330 cards with the M8315? I also have a question about the diagnostic paper tapes. Does anyone have a ROM emulator or other way to load the diagnostics without using a PT reader? Yes, I know there are some SIMPLE diagnostics that can be loaded diagnostics. In fact, I'm wondering if anyone has tried burning the diagnostics into PROMs and installing them in place of the Boot Roms on the M8317 card. Can anyone explain the purpose of the small card that plugs into the back of the chassis near the power regulators? It's not mentioned in the User's Manual and I don't even know it's name. Thom says that it controls the power and the machine will be completely dead if it fails but that's all that I know about it. Joe Joe