From what I've seen the 350s were available with both D-Jet (M116.983 - 8/72-12/75) and K-Jet (M116.985 - 1/76 - 6/80). The early versions had slightly less power (147kW vs 151kW), but they had a higher compression (9.5 vs 9) and thus slightly more torque (287Nm vs 285Nm).
The 450s had the same bore as the 350s, but a longer stroke (85mm vs 65.8mm). Early versions with D-Jet (M117.983 - 8/72-10/75) had the same power as the later K-Jet versions (M117.986 - 11/75 - 6/80), but more torque (378Nm vs 368Nm). They also revved 50RPM more than the later units. I'm not sure if this was all due to the emission gear on the later cars...
And so I'll have to check the engine number!