Stanger;
Different engine builders do different things, I have seen very few dip the piston in
oil, I think that was done "back in the day", don't think many do that anymore.........
Your procedeure with clean bores and ATF is just fine.......
All I do after making sure the bores are perfectly clean is give one, maybe two squirts of motor
oil in the bore and smear it around the entire cylinder with my fingers before installing the piston..... I give one squirt on the side of the piston at the rings and then smear it around the piston/skirt.........this way was taught to me by an aircraft mechanic.... his biggest concern was that everything including all the tools (sockets/wrenches) was surgery room clean, and all parts received a light coating of motor
oil before assembly....... can't remember any engine he built that had any problems........
David