Try to brick the fat +12V on starter with the with M6 tapping. If it cranks then You are not getting signal from the key. If the 735 had automatic transmission then you should find the wires which go to transmission selection lever switch, or maybe the wires on the big roun connector are missmatched.

Does the engine crank or just doesn't start? If it cranks then You might have a problem with anti-theft system if the735 had OBC. If so then there is missing +12V on the ECU which then actuates the main relay...Also carefully check the round engine connector (X20). Although it looks the same, there ...

If you feel the shaking in lower gears more the others check the "Guibo" on the output shaft of the transmission, or maybe worn CV joints on semi-axes.

Maybe you should check the Idle control valve. If injection system is Jetronic it should be located on the right side of the intake manifold, and with Motronic on the left side near butterfly. It happen sometimes that the valve gets stucked open and then U get under-fueling, waving idle and slow RPM...