904 overfill? wrong fluid?

Hi guys. Im putting a slant six in my 72 scamp and just put new trans fluid in.the rans is a 1972 904. the Haines manual said the transmission needs 16 pints of transmission fluid. well I got to about 14 pints and then then it started leaking. I am new at this all this so I dont know if this is because I overfilled , because of a leak or because maybe the torque converter is not in full lock up. also, the kid in the auto department said to use atf +3 but but the haines manual says Dexron II or III fluid???? I am totally lost and any help would be most appreciated. thanks guys