Transmission Swap

Hi,

I recently bought a ´68 Dart GT 318 with a broken 904 auto trans. I´m not too sad about that since I want to shift my gears manually anyway. So here is my question. Are there any secrets which I have to watch out for? Which transmissions from what year and make can I easily bolt in and for which ones are bigger changes to do? Are there trannies with different input shafts? Are there trannies with overdrive and how do I recognize them? What clutch should I take and what pedals and linkage fits - can i take the pedals from a B-body, too?

I appreciate every answer that helps me out, since over here in germany the mopar virus isn´t by far spread as in the US and so it won´t be too easy to find the right parts for a reasonable price.