Harmonic balancer 340

I think the lettering says "Use with 340 cast crank only". As far as I know, there is only 1 cast 340 crank damper.....used in both late '72 and '73??

OP, can you snap and post a pix from the side, showing the relationship between the timing cover and the back of the damper.

Is the problem that the pulleys are too far out to align with the alternator, PS pump, etc? Have you torqued the damper bolt to final torque? It is quite high, like 135 ft lbs.
If you torque on the damper bolt, it ought to slowly pull the damper in with a steady torque level, and without having to go any where near to the final torque level. When it seats, the torque should very suddenly go way up.

If it starts to bind up as you pull it in, then you may be having some interference between the crank key and the key slot in the damper; I would then recommend removing the timing cover and seeing if the damper seats against the slinger and the crank timing sprocket.