65 dart tranny upagrade.HELP

Ok guys, heres my problem. I have decided to upgrade the trans in my 65 dart gt. My donor trans ,( if no one tells me its a wrong choice),is a 904 out of a 76 dodge D100 pickup. Does anyone know of any issues I am going to have with the trans cross member, or will this be the first painless upgrade that I've done,( I'm not holding my breath,lol). There is no question as to whether or not I will upgrade, its a done deal, I would just like to have a little insight before I start.