904 question. Please help.

All T/Flites have a vent in the front pump. I have seen these force fluid out, when using a Trans-brake application. The fix for that is to silicone the vent shut & install a GM style vent in the tailshaft housing.
I doubt that is your problem though. I would check your fluid level when its hot & idling in neutrel.
This is the best way to check your level. An external cooler needs to be added if you don't have one already. You will have more heat due to the loose convertor.
Are you using a quality brand ATF. I prefer a good quality Type-F fluid in my stuff.
Sometimes low quality fluid + mixing types together can cause the fluid to foam & expand, causing it to come out of the vent as well.