M7821 variants

[Noel Chiappa]

So I just discovered that there are three wildly different variants of the
M7821 Interrupt Control card. More here, with images:

    http://gunkies.org/wiki/M782_Interrupt_Control

I'll have to dredge around and see if I can find circuit diagrams for them
all; they are wildly different, the -C has many fewer components than
the -B and -D, and the latter has a couple of delay lines.

    Noel

PS: Sorry about that dis-directed message to Cindy; not quite sure what
I did wrong there.