MO is the engine code for a 1968 302. DZ was used for 1969 only. I believe that the first 302 blocks were two bolt mains, and then upgraded to four bolt mains for the 1969 model year. I am more familiar with 1969 models. Maybe some 1968 Z owners will chime in.
1969 SS Garnet Red X55 350 Factory 4 speed
12 Bolt 3.55 Posi
461 BBC TKO600