u would leave the front two in. most quads nowadays have the rear pair running parallel to the stringer and using two centre fins, leaving in those two, unfoiled and not offset would give u a fast board that will be a dog to turn on.
Also advisable to considerably upsize the fins if you are going to run it as a twinny. does your board have four or five sets of plugs ? And - is the wanting to go twinny a bit of a fun experiment or are you trying to get something else out of your board that you currently dont.
cheers
