Need a 4-Speed

I think I will be able to differentiate between an OD and non-OD (thanks to Outlaw), now my question has to do with installation. Will the 4 speed bolt right up to the 3spd bellhousing or do I need to yank the bell housing from the lucky 4spd donor (providing I find one)? And are there any special alignment considerations (something like a steering shaft where they have to be aligned correct to function properly)?
Thanks for the help.