So, thanks to you fellows advice, I have been able to replace my logic board in my g3 blueberry 350 slot loader. I put a new 500mhz board in and it went smoothly, I had to modify the heat shield at the back with tin snips so the VGA or whatever would stick through. works great.
Anyway, I also have an indigo g3 400mhz with fire-wire ports on the side. My blueberry does not have these firewire ports. So my question is: Is there a way to switch the fire wire ports between the two, or am I better off sticking the faster logic board in the imac with the firewire ports?