Thanks for the reply. I have had a look at Partsurfer for other bits.
Reviewing the list for the Processor shows that the 640 I have is the best processor mentioned. I think because the 641/651/661 came out about a year after mine (the D0's have N/A for date, so may be later) they are not mentioned for my computer. So, I'm hoping that someone with some technical knowledge of these processors can tell me they are compatible. To my semi-trained eye, the specs appear very similar, except for the lower power of the 6x1's. As voltages are very similar (1.2-1.4 V vs. 1.2 to 1.325 V) I'm hoping that isn't an issue, and that the system will recognise the new processor. I need a pretty definite answer as it will take quite a bit of disassembly to get at the processor, and I don't want to have to do the job more than once.
My follow up question, once this is resolved, involves the buying of a used processor off ebay, and what to look out for.