I have both 73 & 74, they are definatly different, the mounting brackets are different also, the bumperetts hold the inner brace to the bumper on the 73 & they bolt right to the brackets together with the bumper bolts. On the 74 there is an extra hunk of metal on the inner brace , inner mounts to the brackets & the bumper bolts to the inner brace & not directly to the mounting brackets, the angle of the brackets is also different.
Not great pics but something
pic 1 73 bumper in primer, 74 in beat chrome
pic 2 extra metal on reinforcement
Hope that helps,Rich.