differnce between 1966 904 trans and 1967

i have a 1966 dodge dart nicely built 360 and im mating my stock 904 to it. my problem is finding performance rebuild kit and stall converter. i can get 1967 and up, but 1966 and down cant find. I just want to know what is the difference between the two.
and where to find a performance rebuild kit and a stall converter with out giving up my first born son! thanks for any advice