they are the same 273-318 from 1966-1972 on all B,C,E as they all use the same rubber motor mount insulator....right and left interchange.
the steel brackets are left and right sensitive meaning there is a drivers side and a passenger side steel bracket.73 c-bodies stayed the course with those brackets also....not changing to spools till 74. now getting into the 340-360 engine series.....using 273-318 mounts....on the passenger side bracket....using 273 passenger side bracket on 340-360....you have to drill one hole straight across the bracket.the passenger side 318 bracket is a direct bolt on to 340-360 blocks...the drivers side 273-318 bracket will bolt on to the 340=360 engine blocks. all the ears line up to the corresponding holes in the steel bracket.however on one ear on top there will be a gap between the ear of the block and the inner flat of the bracket.easy way is bolt the steel bracket to the ears of the block with the two that are fluch.fill in the gap with washers or a homemade spacer.tighten. the above information is for B,C,E bodies not A.