I guess I should update this thread with info about this upgrade being done on PowerBooks... Short story is, it doesn't work. I tried doing the same 740 swap on a PowerBook 3400C, and while it did chime, it did nothing more than that. No video, and no boot. Re-installing the original 603 restored functionality. I can only assume at this point that there is some check in the system firmware that needs to be patched, similar to what needs to be done when doing a 7448 upgrade on some of the later machines. Unfortunately, in the case of these old-world ROM machines, the BootROM is not editable, as they utilize mask ROMs to store the ROM content. I'm not sure if it'd be possible to replace the 4 ROMs with standard EEPROMs, but at this point I don't even have a dump of the machine's ROM to look at. If I had a dump available, I could most likely figure out the issue and patch it (assuming a check in the BootROM is indeed the cause) relatively easily.