Fuel injector pump replacement 300 TDI engine – please help.

[slon4eto]

Hello to everyone.
I am new to the subject with the fuel injector pumps.
For better reference see all pictures I applied.

I have a 1997 300TDI with EGR Land Rover Defender 110 Hardtop.
My engine is a 21L (see images below), EGR is blanked, not removed.
I have no immobilisation. There is an iron rope/ linkage between the throttle and the pump itself.
The numbers on my fuel injector pump,s shield with an EGR device are: 
Bosch 0 460 414 099     ERR4046.

My questions are:
1) It is possible to replace it/interchange it with a Bosch 0 460 414 093  ERR1985 (see images below).? Will my car run smoothly? By doing so is there any possibility for ruining my engine?
This pump comes from a freshly removed still running engine and I know for sure that it is functioning properly (see pictures for more reference).
2)   I  notice that between the pump body and the engine block itself on my original pump there is a linkage with a spring (see picture) and on the one that I potentially will fit there is no such spring.
What is the role and function of this spring. Could it be that the previous owner could have removed it, or the pump was manifactured by Bosch without this spring for a reason?

Every personal experience, advice and explanation would be much appreciated.

Thank you in advance for your answers.

[Eightpot]

Hi - yes you can use the ERR1985 with no problems.  This was fitted to Discoveries, the only difference being a slight difference in maximum governor rpm. It will not affect your engine as long as the pump is in good condition.