68 dart questions,"engine transplant"

The 8 3/4 rear will bolt right in. As far a hood clearance, it might be tight. Maybe you could pop the rear of the hood up a little.
The 340 flywheel and clutch will bolt up to the 318 if you plan on putting it in the Duster for now. The roller pilot bearing will allow you to use the 318 with a 4spd. A SFI flex plate is fairly cheap, but the convertor and trans will probably cost a bit.
The 295's will be way to big for the Dart. 245's will probably be the widest you could use (like Mike).
Leave the Dart a small block and big block the Duster. You'll need the drivers side motor mount bracket for the 340 when you put it in the Dart. If you decide to do it, let me know and I'll send you the brackets. I have two extra sets. You'll just need to get the rubber isolators. Or you could go solid :thumrigh: