69 should have a Steel crank all of them did .
But it has been 47 years I highly doubt anyone would install a cast 340 crank in an earlier 340 but strange things do happen , if it needed a donor crank at some point you could use a steel 318 crank which is much more common & add weight to balance for the 340 .
SO assuming it runs & doesn;t vibrate it is balanced & it should have a 1" thick damper on the front , cast rank used a thicker damper clearly marked for cast crank on the front face
