Thank you all for your help. I haven't managed to get back to the project yet, just wanted to let you know I appreciate the insights.

I plan to create a prototype pcb for a 89c52/external memory setup, likely 32K each of parallel eeprom and RAM for data memory (for now, I think my projects will work fine with the 8K internal code memory). I have some 74hc573s I plan to use - I couldn't with the breadboard since they're SOIC and I had no handy way to adapt them.

What I plan to do is include pads for a pullup SIP network alongside the port 0 pins (very handy that they are right next to the VCC pin), as well as one for the ALE line. Then, I'll test the board with no pullups installed and see if it works. If it doesn't, I'll try installing the pullups to see if they help.

BTW, I don't own much in the way of diagnostic equipment, I'm just a hobbyist messing with this stuff on the very very cheap. I may be able to finagle access to some good equipment at the nearby university, but for the moment I don't even have a scope. I'm not flying completely blind; I've got a computer science degree from a school that heavily emphasized the EE dimension, and have been playing with microcontrollers off and on for years. Never tried any circuitry quite this complex before, though.

Thanks again.