The difference between the 273 and 360 mounts is just the left side. The ears are about 1/2" different width. You can use shims to take up the clearance if you really want to, but the proper mount would be better.
I believe that you can just use the stock 68 340 left mount and it will bolt up and line up correctly.
You also need the correct oil pan to fit, here's a link with that information, see post #10 and beyond...
http://www.forabodiesonly.com/mopar/showthread.php?t=295405&highlight=360+oil+pan+early