Since you have already invested in the FCC, what do you have for a return line from the FCC to the tank? I know they call it a vent line, but if you read all the instructions and user comments it's clear it's a return line and not just a vent. With a good unrestricted return others have gotten the FCC to work. You will need a return if you go in-tank anyway, so why not try it first?

I went with the in-tank setup for my 64 after reading the comments on the FCC. Had to modify my existing tank to put the Aeromotive Phantom 340 in it.