Why do 86-87 603s need a vacuum amplifier and temperature VSV? I don't see these devices up to 85 and in 603s from 92. I know it has something to do with adjusting the vacuum signal based on coolant temp and boost, but why was this not necessary previously or after?

Do 2.5s and 350SD/Ls have these devices?

Is it possible to fit a pre-85 or 92-on modulator to an 86-87 Diesel and bypass the vacuum amp, if only for simplicity?

Thanks,
Sixto
87 300D