Yes, the PRAM battery was included in the swap, but I had already replaced it with a new one in the original IIcx. I don't think the battery is the problem.

And yes, SIMMs are loaded in full groups of 4 matched sets -- 4 x 4 MB and 4 x 1 MB. If I remember correctly, it was only the Mac II that couldn't handle SIMMs >1 MB in the first four slots.

I like your fast and furious interrupts theory. In fact, I think it may be right on. But the vexing part is my inability to ascertain the source of these mythical interrupts. I know there's no unusual extension or control panel causing the problem because the problem is exhibited under a fresh 7.5.3 install.

So, to sum up: the problem occurs under a fresh install on two different IIcxes. The problem does not occur when the exact same drive is dropped into a IIci or LC III. This seems to eliminate a software problem, unless I'm missing something. Then, a fresh PRAM battery is being used with RAM that is confirmed good in a IIci and neither IIcx motherboard shows signs of physical corrosion or damage. This seems to decry the hardware issue. I'm at a bit of a loss here . . . :-/