I take it this is a rare jet hydro not a tunnel. The jet hydros were not all that great because you could not get them to ride on the sponsons. Turn fin was added as you say to help with left turns since that is the way you turn primarilly out on the river.  Fins on both sides will certainly help with what you want to do. The old hydros (v-drives) all had them back in the 70's just saw Prowd Mary at Long Beach fully restored it ran them on each sponson. If you take the one off you won't be able to turn well ether direction.