340 Motor mounts

I just put a 360 in a 74 Dart with the same problem. The 340/360 ears on the driver's side are about 1/2 inch narrower. Chrysler used to make a narrower mount for the 340/360 then they quit stocking it. I heard later that Chrysler made a shim plate so that they could sell the 318 mounts for the 340/360.
All of the auto parts stores now just sell the wider 318 mount as a 340/360 mount. I put a couple of spacers between the 360 ears and my 318 mount and it bolted in pretty well.

BTW, those 71 A body 340 mounts are GOLD these days. Used ones go $75-$125 so don't throw them out!