I have a 1979 chrysler 700 skier, engine number 709H79a. I was looking for a water pump kit for this. Some that I have found have 12 blades on the impeller and some have 6. Is it ok to use either one, is one prefered over the other? I would like to have the correct one in hand before pulling the lower unit off. I am not sure which one is in there now. Thanks in advance!