You can have a lot of atf in there. As long as you don't run it hard or put too many miles on it you're fine. ATF is an amazing way to clean tarnish or even hone a cylinder bore... if those rings aren't sealing right, they may seal better after good run with ATF. ATF is almost the same as conventional motor oil, except it has way more cleaning agents and less wear and tear additives. Keep the quantity to a minimum, as well as the run time and nothing will be hurt. Oh, and it won't need to be done often, a little ATF goes a long way.
