904 trans leaks

Hi all, my 904 trans is leaking out of the pan. Was gonna replace the pan gasket and the filter while in there. How much trans fluid should I get and what kind? I am not flushing it, just replacing what comes out.
http://www.oreillyauto.com/site/c/s...ear=1972&make=Plymouth&model=Scamp&vi=5144995