72 duster /6 to sbm swap help

For starters you'll need a 4 speed hump, shift mechanism, shifter handle, shift rods and the correct yoke. You said the 4 speed was out of a roadrunner so you need an a body length tail shaft housing.
Next you need a manual transmission brake and clutch pedal assembly. Bell housing, clutch, flywheel, pressure plate and throw out bearing. You'll need a pilot bushing or bearing as well so you need to make sure the crank in the 318 is drilled for that as well. Then you'll need an a body z bar, ball studs and brackets for both the engine side and the body side, z bar bushings and springs. You'll also need the right clutch fork and pivot for your bell housing.
For swapping in the 318 swap the k frame get a new radiator with the right hoses. You'll have to get new battery cables and change some wiring lengths in the engine bay. If the 318 does not have all the brackets and pullys put those on the list too. I'm not sure if the center link is different from a slant to a small block so check into that. When I got a small block k frame I got the center link that came with it.