Complex sentence: The final constraint was due to the light body build of Japanese people at that time, after examining the M36 Jackson, 90 millimeter ammunition was felt to be the upper limit of what an average Japanese tanker could handle effectively.
Split into simpler sentences: The final constraint was due to the light body build of Japanese people at that time. After examining the M36 Jackson, 90 millimeter ammunition was felt to be the upper limit of what an average Japanese tanker could handle effectively.