What are you really referring to with the "mechanical" part? The control?
VP44 is a mechanical pump with the electronic control or EDC. As its design of radial pistons (VR/VP series) instead of axial (VE series) as previous it has much higher injection pressures ~700 bars vs ~400 bars which means doubling the power output per cylinder e.g. from 25kW to 50kW.
VE pumps have mechanical control/governors but they also come with EDC(essentially same control design as VP44) later but I'm not sure you could fit one instead of VP series.
Because of higher injection pressures you'd have to replace injectors as well.
Regards