I can't tell for sure from your photo but if it has the whole rear edge of the choke well open, it's the '73 up manifold. That manifold has the big round weight and a 3/8" center stud going up through the intake manifold. A '68 manifold should have a smaller section open just on the RR corner of the choke well. You can close the opening off a bit on the later ones with some sheet metal if you find the choke doesn't heat up quick enough. The '70-2 manifold has a choke well that opens into the exhaust and takes a stamped steel cup and gasket to seal it off. The choke then mounts on top of that.