Thanks for the input. I'm digging as fast as I can.
First, some ancient folklore said memory cards should go from the inside out, e.g, slot 1: 128 MB, slot 2: 64 MB, slot 3: 32 MB, etc. This is where I was headed. The folklore may be useless, and I plan to try some other options as soon as I can get to it. It's very difficult to reach the cards in this old Compaq sucker, so I have to take it slowly.
Second, I was also wondering about the 64 MB max per slot constraint. The literature I have is a little fuzzy on that, but if that's the case, I won't go buy two more 128 MB cards to max it out.
Third, Belarc Adviser reports the Main Circuit Board as:
Board: Compaq 05E4h
Bus Clock: 100 megaherz
BIOS: Compaq 686U2 04/26/99