360 to 904 sorry confused

I don't post much but I need help. I have a '74 dart swinger 318/904 tranny . I have searched and only get confused with the flex plate. Yes, I know it has to be balanced. I have a 2002 magnum 360 300hp crate motor still in the crate. I want to put it... guess where... yes, my swinger. :burnout:
From what I have searched there is only one flex plate that fits this motor and is no longer made by B&M. Do I look for a 727 or find the correct flex plate and torque converter? Sorry for asking this ? again. I know it's been talked about at times but I am looking for more details. Thanks for your help.