Ideally you'd want to compare the PCB of both the 180Mhz part to the 240Mhz part - to see if a block of resistors exist that allow you to adjust the mutiplier. Since most 603e-era Macs are overclocked this way, I'd be hopeful that this is the case.
On the other hand, with the 2400c being very similar to the 3400c, the only thing I could find on 3400c overclocking was on replacing the clock crystal (perhaps easier to achieve?):
http://www.danpalka.net/hooper/
Another consideration is the 603e's don't overclock that well, so even if you did find a way to do this, overclocking the stock CPU will only give 10 - 15% increase at most. As for replacing the CPU - so you have access to an SMD rework station?
With regards to your faulty power board, the same SMT fuses that cause the infamous "GLOD" on 2400c also exist on the power board, so run a continuity test over them to see if they are working or not.
Do you have any pics of your prototype 2400c? Love to see it. I was lucky enough to repair two 2400cs earlier this year (required painful SMT fuse replacement), and kept one, which has become my most treasured Mac of all - very very few in Australia.
JB
On the other hand, with the 2400c being very similar to the 3400c, the only thing I could find on 3400c overclocking was on replacing the clock crystal (perhaps easier to achieve?):
http://www.danpalka.net/hooper/
Another consideration is the 603e's don't overclock that well, so even if you did find a way to do this, overclocking the stock CPU will only give 10 - 15% increase at most. As for replacing the CPU - so you have access to an SMD rework station?
With regards to your faulty power board, the same SMT fuses that cause the infamous "GLOD" on 2400c also exist on the power board, so run a continuity test over them to see if they are working or not.
Do you have any pics of your prototype 2400c? Love to see it. I was lucky enough to repair two 2400cs earlier this year (required painful SMT fuse replacement), and kept one, which has become my most treasured Mac of all - very very few in Australia.
JB