Hi,
I have an A3640 in my A3000T and it is compiling code 3 times faster now than with the original 68030/25MHz. So I would say it is worth the work.
> On adding a CPU fan, what size is the CPU? Roughly a 486?
Yes, a 486 CPU-fan would fit, but you will have problems to add the fan to the heatsink in an A3000 desktop: There is no space below the drive bay :-(
Noster