318 out 360 in

73 Duster would have spool mounts. Yes the washer thing on the drivers side mount to make up for the different spacings on the block ears between the 318 & 360 still applies.

You will either need a weighted flex plate or torque convertor or if it's a manual weighted flywheel. The 360 is an external balance engine and the mentioned items have a different balance factor between the two engines.