I believe your suspicions are correct - the DZ is definitely larger that the previous date code characters. look at the bottom of the "D" in relation to the previous character - obviously slightly larger. I can't say it's incorrect, but it would bear a closer examination.
Nice car, but why would you spend all of that time and money in a restoration like this, and then put the wrong shifter in it ? If you wanted to get away from a wobbly slip fit cushion, buy the reproduction bolt on with the correct round handle -
Regards,
Steve