Yup, I've had my share of working in the driveway before we bought our current house a few years ago. Nothing wrong with that. If you get the motor/tranny combo, you won't have to worry about the input shaft. Otherwise its not a big deal. I think it was about 5/8" that had to be cut off. I...
I did an auto to 4speed conversion on my 70 Challenger. There's a few extra steps than with a GM, but not a terribly hard job. The one thing you'll probably run into if you do it is Chrysler made auto and manual cranks, so the hole in back of an auto engine crank isn't drilled out deep enough...