318 Cam Maybe Not

Ma Mopar had a specific cam for the 4 speed 340 in 68. From 68 on they used the 340 automatic cam for all the 340's till ???72 maybe? I believe the 340's had a looser converter. There's that slippery slope again. A 340 cam in a 318 makes it idle rougher and needs a looser converter and/or gears.